The Twin Dilemma:
ep 1 -	Hugo tells the Commander that Professor Sylvest found "a dust-like deposit on the floor of [the twins'] room; he says it's zanium." In fact, Hugo just made that up – Sylvest simply said straight out that it was zanium, without any "dust-like deposit" embellishment.
ep 1 -	Watch Elena's monitor screen just before she taps some keys and gets the display of information about the X.V.773 freighter. It's filled with a mass of tiny text which initially looks like just gibberish – but if you look closer, you'll see it's actually the computer program (written in an ancient version of BASIC) to create that information display! Somebody's even typed in the RUN command at the bottom of the screen so that all the actress has to do is press the ENTER key and, hey presto, instant faked information readout!
ep 1 -	After the Doctor and Peri study Titan 3 on the scanner and prepare to go out, the Doctor heads straight for the door without bothering to operate the controls. Then we hear the scanner-closing sound effect, even though neither the Doctor nor Peri are near the console.
ep 2 -	As the Doctor and Peri prepare to go out onto the asteroid surface for the second time, the Doctor again heads for the door without operating the control. Thankfully, Peri says something else and the Doctor turns back for a few more lines, before finally going back to the console and hitting the real door control.
ep 2 -	The silver computer terminal in the safe-house on Titan 3 is prone to wobbling – an obvious example being after Peri spots the bomb ticking away outside the room, and the Doctor walks away from the terminal to have a look.
ep 2,3 -	Why does Peri end up back in the TARDIS when the revitaliser machine sends her ten seconds back in time? Come to that, why does the Doctor find himself in an empty console room if he was sent just ten seconds into Peri's future?
ep 3 -	Mestor could have saved himself the bother of kidnapping the genius twins (and saved us the pain of watching their excruciatingly wooden performance) – the "advanced mathematics" that he forces them to perform are so elementary that Peri could have done them.
ep 4 -	The idea that the other two planets couldn't share the same orbit as Joconda because they're smaller than it is complete rubbish. The mass of a planet has nothing to do with the stability or otherwise of its orbit. And the statements that a planet falling into Joconda's sun would cause it to explode, or "tear a small hole in the Universe" are nonsense, too.
ep 4 -	In the final scene on Joconda, where Peri is saying goodbye to Hugo, you can glimpse the Chamberlain lurking in the background, waiting to come up to say his final line. Somebody off-stage obviously signals to him that he's in shot, since he raises his hand in acknowledgement before moving off out of camera range.

Attack of the Cybermen:
ep 1 -	In a couple of the early TARDIS scenes a scorch mark is visible on the console room wall, next to one of the pillars. However, this mark isn't supposed to be there until Russell accidentally fires a Cyber-gun at the wall at the end of the episode.
ep 1 -	When the Telos work party member (played by Pat Gorman) gets shot by a Cyberman, he knocks the camera as he tumbles down the hill, causing the picture to shake.
ep 1,2 -	In the cliffhanger scene, the TARDIS doors are open (obviously) as several Cybermen enter with Lytton and Griffiths, while Russell attacks (and is killed by) a Cyberman already in the ship. The very next shot shows the intruders standing near the now-closed TARDIS doors – but there was neither time for them to close, nor was the usual door-closing sound effect heard.
ep 1,2 -	On both episodes, designer Marjorie Pratt's credit has obviously been crudely inserted into the end titles sequence, as it causes a noticeable "jump" in the starfield background. [Apparently her credit was initially omitted by mistake, and had to be hurriedly edited in later.]
ep 2 -	The guard-railing on the tomb set seems to be rather flimsy during the struggle between the two Cybermen – it wobbles badly as one of them knocks it.
ep 2 -	When Lytton stabs the Cyber-Controller, his "blood" spashes onto the camera lens.
ep 2 -	In the "fight scene" between the Doctor and the Cyber-Controller, the carpet on the studio floor (under the central console) gets kicked up and rather badly creased.

Vengeance on Varos:
ep 1 -	After the TARDIS breaks down, the Doctor and Peri can be seen standing over the console reading the manual, even though it's clearly just a book full of blank pages.
ep 1 -	When Maldak shoots at the just-arrived TARDIS on Varos, Peri says, "Why did that man fire at us and then turn away as if we didn't exist?" However, after Maldak's initial shot, the Doctor closed the scanner screen, so Peri never got to see his reaction.
ep 1 -	After the Doctor frees Jondar and they are being chased through the Punishment Dome, the Doctor tells Jondar that if they could get back to the TARDIS they could escape easily enough. Peri confirms this. How? The reason they came to Varos in the first place was because the Doctor needed Zeiton-7 to fix the non-functioning TARDIS. Sure, they'd be safe inside the TARDIS, but they wouldn't actually be able to escape from the dome.
ep 1 -	If the illusion of a desert causes thirst, why doesn't the illusion of water quench thirst?
ep 1,2 -	When the Doctor removes his coat in the "desert," the waistcoat he was previously wearing beneath it has suddenly vanished, replaced by a pair of question-mark braces. Later on, after the Doctor has recovered his coat from the acid bath room, the waistcoat mysteriously reappears.
ep 1 -	Compare the first two votes – notice that the cuffs lock around the Governor's hands at different times in each one.
ep 1,2 -	The close-up of the Doctor shows him clearly still breathing and moving, despite everyone watching in Prison Control being convinced that he's dead.
ep 2 -	When the Doctor releases Peri from the transmogrifier platform, the buckle of the restraining belt comes loose and slides slowly down to the bottom of the platform.
ep 2 -	The edging around the acid pool is loose and flaps around during the Doctor's struggle with the guards.
ep 2 -	When the Doctor and co. are in a patrol buggy and get fired on by some guards, they zip around a corner as an explosion goes off near them. Unfortunately the explosion happens at floor level, nowhere near where the guards' shots went.

Mark of the Rani:
ep 1 -	When the Doctor and Peri are left in Lord Ravensworth's office with the guard dog, the dog's position shifts instantaneously between shots – one moment it's in full view, the next it's mostly concealed behind the open door.
ep 1 -	When the dog runs out to attack the Master, it's quite obvious that it isn't barking in the first shot of it trying to climb up the gate, despite all the racket on the soundtrack.
ep 1 -	When the three miners attack the Doctor and one falls down the pit, a later shot still shows three men with shovels attacking the Doctor.
ep 1 -	Just after the Master takes the Rani's parasites, the supposedly unconscious man in front of him blatantly lifts his leg. Also, a very obvious boom-mike shadow is visible as the Master moves away.
ep 1 -	When the Rani leaves the bath house to find the Master, Peri sneaks in to rescue the Doctor, taking special care to bolt the door on the inside after she enters. But when the Rani and the Master return, they just walk in, the door having mysteriously unbolted itself.
ep 1 -	The real Luddites never attacked coal mining machinery, as it didn't threaten their livelihoods (which was the whole point behind the Luddite movement).
ep 2 -	Watch Nicola Bryant stumble and nearly fall as the tree seizes her.
ep 2 -	In the climactic scene in the Rani's TARDIS, a jar containing a baby dinosaur is supposed to fall off a pedestal and shatter. If you watch carefully, you'll see that a lever of some kind is surreptitiously pushed under the wall of the set and gives the pedestal a quick push to tilt it over!

The Two Doctors:
ep 1 -	When the second Doctor materialises the TARDIS on the research station, he and Jamie head for the TARDIS door, with every intention of leaving – but the door isn't open, nor has the Doctor gone to open it. The Doctor then conveniently remembers that he should "take the recall disk" from the control console. It was a prop needed for the story, so it wasn't just an excuse for going ack to open the door (there's dialogue during this as well). He walks back to take the disk, and only then opens the door.
ep 1,2 -	Robert Holmes unwisely directs the viewer's attention to a point that's best left unexamined – namely, how is it we can understand what these aliens are saying? – when Do±a Arana recognises Shockeye's language as being English. Also, in Part 2, the Doctor reassures Peri when she says she doesn't speak Spanish – "That's all right. Neither do they..."
ep 1 -	The space station wall is very shaky as the Doctor and Peri climb into the service duct.
ep 1,2 -	When the unconscious Doctor falls onto some cables, the uprights supporting them wobble very badly.
ep 2 -	When the Doctor interrogates the space station computer, he sets a mass of text scrolling up the screen. If you examine it frame by frame, you can find hidden among the technobabble an error message produced by the BBC Micro program that generated the text: "String too long @ 720".
ep 2 -	At one point, the Doctor delivers the line "Small though it is, the human brain can be quite effective when used properly" and pats Peri on the head. Imediately following that, you can distinctly see a visably angry Nicola Bryant mouth "A**hole" under her breath and then move on to her next line as if nothing were wrong!
ep 2 -	The barely-attached Sontaran collars are a problem all through this story. See especially Stike's confrontation with the second Doctor, when he is leaning over Troughton.
ep 2 -	When the Doctor eavesdrops on Chessene and Shockeye, the hacienda window is open. Then when he makes a noise and Chessene comes over to investigate, the window has mysteriously closed itself. She has to open it, take a look out and then close it again.
ep 3 -	When the Sontarans are attacked by coronic acid grenades in the cellar, one of the Sontarans holding his head in agony does so a bit too tightly – look closely and you can see his head starting to cave in.
ep 3 -	When the Second Doctor is running to hail the lorry, he slips on the gravel of the roadway.
ep 3 -	When the Doctor, Peri and Jamie spot the truck in Seville the Doctor comments "they can't be more than a minute ahead of us". Now, even if the three travellers had managed to stay a minute behind the truck then they'd still have had to run all the way! A Time Lord might be able to manage this but what about poor old Jamie and flappy-arms Peri? Besides, if the Second Doctor and Shockeye were only a minute ahead of the other three then how did they manage to get through the traffic, park the lorry and get out of sight so quickly?
ep 3 -	Just before Oscar is stabbed by Shockeye, you can see through his (very thin and presumably cool) shirt that there is a small bag of fake blood ready for Shockeye to plunge his dagger into. Despite this, it's not very good fake blood, as it doesn't even stain the knife!
ep 3 -	After all the mayhem of Oscar's protracted death scene, Shockeye storming out and the second Doctor having to be helped out of the restaurant, the waiters and other diners can be seen in the background calmly continuing with their normal business! Absolutely unbelievable.

Timelash:
ep 1 -	Watch for the moment when Maylin Renis (one of the Karfellans) accidentally pulls a dial off the computer console. But being a consummate professional, he quickly reattaches it without looking or drawing a great deal of attention to it.
ep 1 -	When Renis is killed by the Borad, his skeleton brings a piece of string down with it as it collapses to the floor. (This was holding the skeleton upright, before a stagehand released it to make the skeleton collapse.)
ep 1 -	Shortly after this, Tekker tells Vena that her father suffered a "fatal seizure". Unfortunately for the writer, medically there is no such thing as a "fatal" seizure.
ep 1 -	The Doctor says he is "travelling light this time" after Tekker's enquiry as to whether Peri is his only companion. But later on we find out that the last time he was here (as the Third Doctor), he only had Jo Grant with him – so wasn't he travelling light then too?
ep 1 -	The TARDIS console's electrical cable is visible in the scenes where the Doctor is taking Vena back to Karfel.
ep 2 -	After the rebels take control of the inner sanctum, several guards lie on the floor, supposedly unconscious. Except for one, who quite noticeably shuffles his legs!
ep 2 -	The "crystal" protuberances of the Timelash interior are clearly held together with adhesive tape. Not to mention all that tinsel scattered around... [Who says the Borad is evil? Someone so full of the joys of Christmas can't be all bad...]
ep 2 -	How is it that the Doctor needs to be secured by a rope to safely enter the Timelash, but Herbert and Mykros are able to enter and clamber around inside without any problems? [Insert your own "fat Colin" joke here.]
ep 2 -	During the attack on the sanctum, the guardolier who shoots out the wall (revealing the painting of the third Doctor) then immediately keels over for no apparent reason – no-one is seen to shoot at him, and no gunfire sound effect is heard.
ep 2 -	The metal railing in front of Herbert's hiding-place overlooking the Borad's lair wobbles several times.
ep 2 -	The small communications console in the sanctum slides all over the floor when Mykros and the Doctor use it to talk to the Bandril ambassador.
ep 2 -	When the Doctor and Peri enter the TARDIS, as the inner doors open, you can see one of the doors bounce off the console room wall and start to close again.
ep 2 -	In the padding scene with Peri and Herbert in the TARDIS (recorded sometime after the rest of this story), Colin Baker's hair is noticeably different (i.e. longer) than elsewhere in the story.

Revelation of the Daleks:
ep 1 -	When Takis and Lilt show a Dalek their security passes, you can see the head of the Dalek operator through its neck grille.
ep 1 -	During the same scene, the actor playing Lilt clearly has difficulty getting his pass out of his pocket. By the time he finally produces it and holds it up for the Dalek to "see", the Dalek has already turned to leave!
ep 2 -	In the very first scene of the episode – who's that bloke walking past in the background?
ep 2 -	Tasambeker stabs Jobel with the syringe without pushing in the plunger, but in the next shot of him, the plunger is fully pushed in.
ep 2 -	When the DJ fires his ultrasonic gun the first time (while showing off to Peri), he shatters the doors to his studio. Later, when the Daleks advance into the studio, the miraculously repaired doors open as they approach it.
ep 2 -	When Davros is hovering above Orcini, the base of his chair is partially transparent, and Orcini's legs can be seen through it.
ep 2 -	When Orcini pushes Davros away from him after Bostock has shot his hand off, he leans back against the control console and pushes it out of position.

The Trial of a Time Lord:
ep 1,2 -	On a couple of occasions we cut to the court room as the Matrix replay is suddenly interrupted, but the Inquisitor and the jurors are seen to be already facing forward (i.e. away from the Matrix screen). A good example is at the end of Episode 1, when the Valeyard stops the evidence just as the stoning starts.
ep 2 -	The wall of the prison hut wobbles as the guards force Peri inside to join Glitz and Dibber.
ep 2 -	Grell's helmet light is sensibly turned off in the shot where he's lurking in the background, eavesdropping on Merdeen and Balazar, but as he turns away and we cut to a close-up of him, the helmet light is suddenly on again.
ep 3 -	Drathro tells Humker and Tandrell that "only part of the planet was consumed by fire" when they wonder about the vegetation on the surface. Yet only a little later, he contradicts himself by saying, "All life was destroyed by the fire"!
ep 4 -	When Katryca leads her people into Drathro's domain, the main doors of the Immortal's castle can be seen in the background behind the group, closed. Yet in the next shot, they are wide open as Humker and Tandrell run out (leaving them open). Then, after Drathro kills Katryca and Broken Tooth and dismisses the survivors, the main doors are closed again in the background.
ep 4 -	As Dibber fires at the wall of the food-processing chamber, the pre-cut section that will explode away is briefly visible.
ep 5 -	The information notice on the TARDIS is absent in the location shots.
ep 7 -	Watch out for the moment when Crozier takes a drink from an obviously empty cup.
ep 8 -	A lightbulb blows as the TARDIS dematerialises.
ep 9 -	There are some very prominent boom-mike shadows visible as the Doctor and Mel are captured by the Hyperion guards.
ep 11 -	Watch the corridor wall next to Mr. Kimber's cabin wobble as Mel leans against it, when she is eavesdropping on Rudge and Janet searching the cabin. Also, when Rudge and Janet leave the cabin we hear the sound of him closing the door, but Mel immediately turns and enters the cabin without having to open the door.
ep 11 -	When Bruchner fires his gun at the Commodore, the ray effect doesn't even reach the Commodore's hand, despite the wound we see later.
ep 11 -	Why does the Commodore state that the Hyperion is hijack-proof, after it has already been hijacked by Bruchner?
ep 12 -	If the Vervoids were genetically engineered, why were they created with stings poisonous enough to kill?
ep 12 -	While the Vervoids are dying, look out for the ones wearing sneakers and tracksuit pants (complete with drawstrings).
ep 12 -	After the Doctor has destroyed the Vervoids, we see a shot of him holding a leaf in his left hand. Cut to another shot, with Mel coming up beside him, and the leaf instantly switches to his right hand.
ep 9,12 -	Somebody moves the TARDIS around between episodes – in episode 9, the bottom of the TARDIS is aligned with the yellow stripes on the floor of the Hyperion's cargo bay. In episode 12, however, the TARDIS is at an angle to these stripes.
ep 13 -	The harpoon shot at Glitz is clearly travelling down a wire towards him, and after impact its shaft bends and wobbles around hilariously, demonstrating that it's just a soft rubber prop.
ep 14 -	In the beach scenes, watch how part of the cloud background abruptly changes as the Valeyard materialises next to the Doctor.
ep 14 -	Watch the scene where the Master and Glitz leave the Doctor in the console room of the Master's TARDIS. You'll note that Glitz and the Master distinctly leave the console room and go into another part of the TARDIS. However, the next time you see Glitz and the Master (talking about the Doctor's imminent switch into a "zombie"), they are definitely standing in front of the scanner screen in the console room. Someone didn't feel like building an extra set for another room in the Master's TARDIS!
ep 14 -	The Doctor tells Mel that 'maser' stands for "microwave amplification and stimulated emission of radiation." It should actually be "by stimulated emission..." [The physicists in the audience have assured me that this is a fairly important distinction...]

Slipback:
ep 2 -	When the Doctor tells Peri he's about to recite his favourite sonnet, "Ode to a Flashist Mud Scavenger", Peri replies that this inspiring title "brings tears to my ears"! [Was this deliberate? Eric Saward corrects "ears" to the more normal "eyes" in the novelisation...]