Revealing mistake: Max Capricorn is a cyborg, with his head being the only remaining part of his original body, wired up to a mobile life support system. If you look closely during his scenes, whenever he turns his head, the costume the actor is wearing to hide his body becomes apparent, as the wires and cables below Capricorn's head also move slightly.
Revealing mistake: In the penultimate scene, with Tim Latimer helping an injured Hutchinson across a muddy battlefield at night, one of the shots is flipped - in the unflipped shots, Hutchinson has his right arm slung across Tim's shoulders, but in the flipped shot, it appears to be his left arm, and the two young men have switched sides. (00:39:45)
Revealing mistake: When the Doctor and Martha get out of the elevator and enter the reception room in search of Lazarus, they pass by the string quartet. The violinist and cellist are only miming the actions of playing, as their bows aren't actually touching the strings of their instruments. (00:18:05)
Revealing mistake: After arriving in New New York's undercity, the Doctor and Martha find a screen playing the news. The Doctor tinkers with it and gets a video of flying cars passing a picturesque view of the city. This is a clip from the last episode set on this planet, "New Earth" - the fact that in a close-up of the screen, the TARDIS can be seen parked on the cliffs as it was in that episode clinches it. (00:03:55)
Revealing mistake: The pyrotechnic mortars used in the destruction of the Family's ship are visible in the shots leading up to their detonation. As the Family run from their ship through the field, the mortars are visible against the branches behind them. Shortly afterwards, they detonate, creating the illusion that the invisible craft has exploded.