The Invisible Enemy:

10ep 1 – When the shuttle first lands on Titan, the Captain moves all the switches towards him to the OFF position — but he misses one, which only goes halfway down.

20ep 1 – Why do the infected shuttle crew kill the men on Titan, when they could just have infected them as well?

30ep 1 – When Lowe presses the DISTRESS button, the entire wall of his office shakes!

40ep 1 – When Lowe is rescued by Leela from the Cryogenics Section, he has frost all over his forehead and almost none on his cheeks. But in his next scene, it has disappeared from his forehead, and fresh frost entirely covers his right cheek!

50ep 1 – The affected space pilot (Meeker) enters the mess room in response to a noise caused by Lowe, and Leela gets him with her knife. Watch the knife in his back when he falls — it wobbles hilariously, and is obviously not stuck in anything very solid.

60ep 2 – Spot the member of the crew walking past in the background in the very first scene.

70ep 2 – At the start of the episode, the Doctor is forced to try shooting Leela: he resists, and the shots go wide. Watch where his second shot supposedly lands — it has nothing to do with the direction he's pointing the gun!

80ep 2 – The establishing shot of the Bi-Al Foundation shows the damage to the asteroid (see especially the large red cross) which doesn't actually happen until later on, when the shuttle crashes into it.

90ep 2 – The door to the isolation ward seems to be amazingly intelligent; on several occasions people stand right next to it exchanging dialogue with others and the door stays closed, yet whenever anyone actually wants to go in or out, the door opens by itself as soon as they come close.

100ep 2 – The reflection of a crew member moving around is visible in the front of the cloning booth in the scene where Leela first meets K-9. Also, K-9 seems to instantly turn around between shots from facing the bed to facing the door and Leela.

110ep 2 – As Leela is scanned by Marius, the supposedly catatonic Doctor in the foreground can be seen moving his head from side to side.

120ep 2 – After a rogue shuttle crashes into the foundation with enough force to violently rattle the whole place and destroy an entire level, we are supposed to believe that Professor Marius finds — intact and undamaged — the infected body of one of the shuttle occupants. I think not!

130ep 2,3 – K-9's ears keep changing their orientation from scene to scene, sometimes not even being aligned symmetrically. They are particularly askew in the scene where the Doctor quizzes K-9 about cloning techniques.

140ep 2 – After K-9 stuns one of the infected doctors, the guy almost knocks over one of the free-standing columns as he falls to the floor.

150ep 2 – According to K-9 in this episode, the first successful cloning experiments were "first carried out in the year 3922". Er... considering Dolly the sheep arrived in 1996, he's only about 2 millennia off!
[Was K-9 using the Hebrew calendar...?]

160ep 2 – Professor Marius collects DNA from the Doctor and Leela in order to clone them. Are we to assume that he also extracted DNA from their clothing? Perhaps this would explain why their clones are fully dressed in identical clothes when they appear.
[Of course, the most likely explanation is that Mary Whitehouse would have had a fit if two naked Doctor and Leela clones had appeared instead!]

170ep 2/3 – The camera is reflected in the front of the cloning booth as Marius picks up the miniaturised clones of the Doctor and Leela.

180ep 2/3 – Apart from the microscopic copies of the Doctor and Leela, Dr. Marius also chooses to inject a syringe full of air into the Doctor's bloodstream at the end of the episode. Rather irresponsible of him, since doing that sort of thing usually causes a fatal embolism!
[Time Lord biology saves the day yet again, perhaps?]

190ep 3 – There's one scene where K-9 has to shoot part of a wall away to block a path, and even before he shoots the wall, you can see the cracks where it's supposed to break away. And the remainder of the wall wobbles badly when the broken-off piece hits the floor.

200ep 3 – When they match up the two sets of blood cells using the viewer, isn't it odd that the organisms are oriented exactly the same way, and are swimming in exactly the same direction? In fact, the two slides are completely identical. What are the odds?

210ep 3 – When K-9 shoots an assailant (who infects him before expiring), notice that the overlay of K-9's laser beam is very badly done. First it appears to be emanating from his eyes, before the camera changes position, making the source of the beam suddenly shift to his snout.

220ep 3 – Speaking of K-9 being infected, we're clearly meant to accept at face value that a robotic dog can somehow be taken over by an organic virus...?!

230ep 3 – When K-9 shoots Leela, she drops cold even before his beam appears.

240ep 3 – Later on, when K-9 revives Leela, the back of the K-9 prop is obviously being held up off-screen so that its probe antenna can reach down to where Leela is lying on the floor.

250ep 3 – When the nurse tells Leela and K-9 what's happening in the isolation ward, there's a lovely upside-down reflection of a crew member in her head-mirror.

260ep 3 – After the Doctor is cloned, his clone is no longer affected by the virus — in other words the virus wasn't copied into his clone. Then Lowe gets cloned and injected, but he's still affected; i.e., the virus was copied into his clone. Why the discrepancy?
[The argument "But he's a Time Lord" won't fly. If the real Doctor can be taken over, then a 10-minute copy of him can be, too]

270ep 4 – When the Doctor runs into the TARDIS after setting the trap for the Nucleus, Tom Baker hurtles into the police box so fast that he knocks it out of position.

Add a new blooper for this story »