Continuity mistake: When Martha and Jenny are washing the floor, just as Hutchinson and Baines come along and tell them off for laughing, one of the lace ribbons on Martha's cap moves between hanging in the back in shots facing her and draped over her shoulder in shots facing the schoolboys. (00:04:15)
Continuity mistake: When Martha initially bursts into John Smith's study after hearing that he fell down the stairs, the door is mostly closed. When she runs back to the door to knock on it after Joan Redfern tells her off for bursting into a master's study unannounced, the door is open wider. (00:06:35)
Continuity mistake: During Joan's encounter with the Family's spaceship, when it shines a beam of green light at her, she shields herself by raising her right arm. It changes position between a wide shot and a close-up. (00:12:20)
Continuity mistake: After watching the Family's spaceship land, Jeremy Baines puts his hand on a tree stump as he walks around it to approach the ship. He does this twice, in two successive shots. (00:14:10)
Continuity mistake: When the Doctor fits the Chameleon Arch watch into the headset, his hands change position between shots. (00:20:15)
Revealing mistake: In the close up shot of the boys' machine guns firing, in the background a white truck can be seen driving across the green countryside; not appropriate for the time period of the story. (00:25:25)
Other mistake: Joan puts her stethoscope in her ears backwards when listening to John Smith's single heart.
Plot hole: The Doctor leaves Martha a recording with instructions for her for when he's human. However, the flashbacks to the incident that led to him using the Chameleon Arch don't leave enough - or any - time for him to have made the recording, presenting his decision to use the device as a spur-of-the-moment one that he immediately acts upon.
The Family of Blood (2) - S3-E9
Continuity mistake: As the scarecrow-soldiers advance on the school to do battle, the scene cuts to Sister of Mine, looking out from a school window. There is heavy rainfall outside. When we immediately cut back to the advancing scarecrows, it is a cold, clear night. (00:10:00)
The Family of Blood (2) - S3-E9
Continuity mistake: When Martha finishes listing off the bones of the hand to Joan, in order to prove that she's a medical student from the future, in a shot facing Joan, Martha's thumb is extended. In the next shot, facing Martha, her thumb is suddenly folded back, as if she was using her hand to display the number 4. (00:12:15)
The Family of Blood (2) - S3-E9
Continuity mistake: When Timothy opens the watch into the girl's eyes, Jeremy Baines shouts "Time Lord", then a few seconds later; "What are we waiting for. Attack!" There is then a shot looking down on the scarecrows, Jeremy and Jenny. If you look closely at Jeremy Baines, it's a different actor playing him. (00:16:20)
The Family of Blood (2) - S3-E9
Continuity mistake: When Sister of Mine enters the school's courtyard after the battle with the scarecrows, her right hand is holding her balloon at the bottom, with the bottom of the string wrapped around her left hand. In the next shot, facing her, her right hand is at her side, with the balloon floating above her left hand. The balloon proceeds to jump between positions until Sister of Mine murders the headmaster. (00:18:00)
The Family of Blood (2) - S3-E9
Continuity mistake: When the Doctor comes back to the Cartwright house after imprisoning the Family, Joan walks over to the window and looks out, clasping her hands in front of her. In the next shot, when she asks the Doctor if it's done, her hands are suddenly by her sides, and she is shown clasping them again. (00:34:45)
The Family of Blood (2) - S3-E9
Continuity mistake: When the Doctor and Martha hug after he thanks her for looking after him, the position of her arms changes between shots. (00:38:20)
The Family of Blood (2) - S3-E9
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)
The Family of Blood (2) - S3-E9
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.
Visible crew/equipment: As Sally enters the living room in the abandoned house, in the shot where she walks through the doorway, a cameraman holding the camera can be seen reflected in the window of the door next to her. (00:00:35)
Continuity mistake: When Sally pulls off the last piece of wallpaper to reveal the writing, "Love from the Doctor (1969)", in the first shot, the second "9" in the date is somewhat patchy, with the middle part of the number mostly gone due to the removal of the wallpaper. In a close-up of "The Doctor" just moments later, the "9" is intact, visible in the lower right corner. (00:02:15)
Continuity mistake: When Sally Sparrow is about to take the key from the weeping angel, at first the key is on a piece of string, and that string is wrapped around the weeping angel's left hand. In the next shot, and when she pulls the key out, the string is now only in the angel's palm. (00:10:30 - 00:11:10)
Continuity mistake: When Sally enters the DVD store looking for Larry, she encounters the store's owner, Banto, who is sitting behind the front counter watching a movie. He holds up his finger to indicate her to wait briefly because of the point in the movie he's at. In shots facing him, his hand is quite close to his mouth and chin, but in a shot facing Sally, his hand is considerably further away from his head. (00:13:10)
Suggested correction: He would have been planning the change to human for a while now, not just made it up on the fly. So he could have made a recording before the opening scene.
The episode makes it pretty clear that he and Martha got taken by surprise by the Family's attack. The Doctor also explicitly says, when he gets out the Chameleon Arch headset, that he never thought he'd use it. The flashbacks consistently present his decision to become human as one made as an urgent, in the moment one.