Continuity mistake: When the Sybilline priestesses kneel after the High Priestess speaks, in a shot from the front, Donna, sitting on the altar, has her hands in front of her - she's using her left hand to take the rope off her right wrist. In the next shot, from behind, her hands are at her sides. In addition, the rope still on her right wrist disappears. (00:27:05)
Revealing mistake: When the Doctor and Donna are walking through the underground tunnels towards Mount Vesuvius, tunnels that can be presumed to be fairly warm due to their connections to volcanic activity, their breath is visible - something that only happens in cold temperatures. (00:31:20)
Continuity mistake: When the Doctor explains to Donna how he sees the universe, the distance between them changes several times. (00:31:40)
Plot hole: After getting out of the Pyrovile escape pod, the Doctor and Donna start running back to Pompeii. In the process, they are somehow able to outrun what appears to be a pyroclastic flow. Pyroclastic flows can reach speeds of up to 700 kph, and should be impossible for them to outrun. (00:38:15)
Continuity mistake: When the Doctor is talking to Evelina at the end, her hair changes position between shots. (00:44:00)
Continuity mistake: When the Doctor and Donna leave as Caecilius, Metella, Evelina and Quintus stand and watch the destruction of Pompeii, the TARDIS changes orientation between shots - in both of them, one from in front of the family and one from behind, the TARDIS' door, with the sign, is visible. (00:45:10)
Continuity mistake: After Metella hands Caecilius the beetle brooch, his hands change position between the close-up and the wide shot. (00:46:10)
Continuity mistake: For most of the scene where the Doctor and Donna find the dying Ood Delta-50, the front of his body is covered in snow. After he mentions "the circle", when the Doctor is asking what that is, the snow on Delta-50's chest is gone. In addition, the Doctor's hands change position between shots. (00:06:25)
Continuity mistake: During Donna and the Doctor's conversation with an Ood at the reception who she approaches to ask if he's all right with being a servant, in shots facing the Ood, he's holding his translator ball higher than he is in wide shots and shots facing Donna. (00:11:50)
Continuity mistake: During the first scene in Warehouse 15, when Dr. Ryder puts his hands on the railing as he looks over it, the exact positioning of his right hand changes between shots. (00:15:05)
Continuity mistake: When the Doctor opens a shipping container full of Ood and he and Donna stand in the entryway, he only opens the right-hand door, leaving the other one shut. In a shot from behind the two of them, facing into the crate, the left-hand door is now wide open. (00:17:15)
Revealing mistake: Soon after the Doctor and Donna are blasted back there is fake snow on the camera, indicating there's a camera there. (00:34:15)
Continuity mistake: When the Doctor and Donna enter Warehouse 15 and see the Ood Brain, the Doctor rests his hands on the railing with his right hand off to his side. In shots from above and behind him and Donna, his right hand is closer to him. (00:35:30)
Continuity mistake: When Ood Sigma steps in front of Mr. Halpen while he's holding the Doctor and Donna at gunpoint and suggests he have a drink, the glass Sigma holds up is empty, despite the fact that he was heard pouring Halpen's tonic into it just moments before. In a shot later in the scene, the glass is shown full. (00:37:30)
The Sontaran Stratagem (1) - S4-E4
Continuity mistake: When Jo Nakashima says, "If you won't listen, I'll find someone else who will," she's holding her purse and bundle of papers in the crook of her left arm. When she opens the door of her car, the items have jumped to her right arm. (00:00:45)
The Sontaran Stratagem (1) - S4-E4
Revealing mistake: In the beginning, the ATMOS system takes the car to the Thames, then runs it into the river. At first, the car runs forward normally. After the angle change, there's a huge white cloud of mist behind the car that dissipates quickly, meaning an air cannon of a sort was used to propel the car into the river. (00:02:35)
The Sontaran Stratagem (1) - S4-E4
Continuity mistake: In the TARDIS as Donna navigates, the Doctor uses a hammer to help correct the trajectory, then rests it on his neck and shoulder. A second later, when the phone rings, his hand, holding the hammer, is suddenly much lower, below his waist level. (00:03:15)
The Sontaran Stratagem (1) - S4-E4
Continuity mistake: When Private Harris orders the two hypnotized workers in the basement of the ATMOS factory to let him through the door they're guarding, he's holding a torch in his left hand, and when shown from behind has that hand down by his side. In the Sontarans' video feed, which also shows him from behind, his left hand is on his assault rifle. (00:11:15)
The Sontaran Stratagem (1) - S4-E4
Continuity mistake: When General Staal surprises Privates Harris and Grey in the room with the cloning tank beneath the ATMOS factory, the position of his right hand, holding his command baton, changes between shots several times. (00:14:10)
The Sontaran Stratagem (1) - S4-E4
Continuity mistake: When Martha asks the Doctor to look at her so she can point out she's not carrying a gun, he's sonicing an ATMOS device, and he lowers his hand when she speaks. In the next shot facing Martha, the Doctor's hand is raised again. (00:16:10)
Chosen answer: 1) When Stephen Moffat took over he ignored a lot of what had been developed before (there is not in-universe answer). 2) It would have killed Rose, so the Doctor absorbed the energy. His body regenerated before the energy could do a significant amount of damage that would prevent regeneration.