Seven Minutes to Midnight - S1-E8
Continuity mistake: When Mohinder is back in India, his mother tells him that his sister Shanti died at the age of 5, when Mohinder himself was 2. In "The Hard Part", Mohinder tells Molly Walker that Shanti died before he was born, and shows her a photo of Shanti (who looks 5 years old) and his pregnant mother.
Continuity mistake: When Matt Parkman gets thrown out of a window by Niki Sanders, he lands at least a few stories down and has a cut upon his head. The amount of blood on his head differs significantly from shot to shot.
(Volume Two: Generations) Four Months Later... - S2-E1
Continuity mistake: When Claire hugs Mr. Bennet she is holding her note in her right hand. In the next shot as she turns around and runs off to school the note is in her left hand.
Continuity mistake: When Charlie invites Hiro over to help celebrate her birthday, the invite is almost immediately after she says "hold that thought" and walks away from his booth. But in that scene in the previous episode, Charlie was already across the room with the other townspeople when she signaled Hiro to come over.
Continuity mistake: After throwing the laptop, when Mohinder takes the key out of the book, the tape is bunched up and stuck to the key, but in the next shot the tape is fresh and sticking out freely.
Continuity mistake: Maya's necklace disappears between shots when she accuses Sylar of killing her brother.
Continuity mistake: When Alejandro finds Maya outside the tunnel, she has black ooze from her eyes running down her cheeks. As he starts his healing, we get a close-up shot of how the ooze fades and disappears from Maya's face. But in the next shot of her face, when she falls forward, the black stuff is back on her cheeks. It's gone again in the next shot of her. (00:29:20)
Continuity mistake: When Meredith and Nathan are talking in her trailer, as he says, "I could have been a much better person back then", he has his sunglasses in his hand and places that hand on the table. Cut to a shot from behind him, and his hand is resting on the table with the sunglasses beside it, with no time to put them down and move his hand in between the shots. Also, when Meredith says, "You and me, we were never gonna work out", his hand goes from being on the table to his lap between shots, once again without having had the time to move it. (00:32:10)
How to Stop an Exploding Man - S1-E23
Continuity mistake: Hiro's sword changes position between the shot in which Hiro arrives to the scene and the shot when he is about to kill Sylar.
Continuity mistake: Right before Sylar shoot Maya, you can see she already has a bullet wound on her chest.
Continuity mistake: When Peter is having his vision of New York, D.L. can be seen picking up Micah and running away. When the camera pans out to show Matt holding them back, D.L. is picking up Micah again.
Continuity mistake: At the end of ep. 1-14, "Distractions", Meredith calls Nathan to tell him about Claire. In that episode he is holding the phone to his ear, with nothing else in it. In the beginning of this episode, when the same conversation is shown, he is holding a pen in the same hand as the phone. Also, in ep. 14 Meredith said to him, "We haven't spoken in a long time, but... Our daughter just found me". In this episode, she says, "We haven't spoken in a long time, but I just had... Our daughter just found me".
Continuity mistake: When Maya is arrested, she starts manifesting her powers on the policeman. In a close-up, we can see the black ooze coming out of her eyes. Cut to a shot from above, when the policeman's eyes turn black and he drops the handcuffs, and Maya's cheeks are suddenly clean again, with no trace of the black stuff. (00:33:45)
Continuity mistake: In ep. 1-14 "Distractions", when Claire asks Meredith about her father, Meredith answers, "Well, that's complicated. Why don't you let me work on that for next time?" But when the same scene is shown in a flashback in this episode, Meredith says, "Well, that's complicated. He's kind of a big shot".
Continuity mistake: When Sylar comes for Isaac the painting of Hiro and the dinosaur is visible in the studio in several shots, even though Hiro took this painting to Linderman several episodes ago. The episode director even comments on it during the audio commentaries.
Continuity mistake: Season one takes place over five weeks. Janice Parkman goes from not being visibly pregnant to being at least five or six months along during the course of those five weeks.
Continuity mistake: Season 2, episode 10, "Truth and Consequences": In the previous episode, "Cautionary Tales", when Noah was brought back to life he regenerated, then sat up, looked around him and said something sounding like "Home". In this episode, when the exact same scene is shown, we see Noah regenerating and sitting up, but this time he just looks straight ahead before lying back down, and does not say anything. (00:05:50)
Continuity mistake: This mistake is repeated in the next episode too. After D.L kills Linderman he is lying face down, his face is flat against the floor and we can see right into the hole in is head, he has already stopped moving. Then after the camera starts to pan around, Linderman's head is now facing right, and we get a good look at his face.
Continuity mistake: In the scene where Mr. Bennet, Matt Parkman and Ted Sprague are at the used car lot, Ted is using his powers to defrost a blue station wagon. As the frost is melting you see "Automatic" written on the windshield. The shot cuts to Bennet and Matt talking by the pay phone. When the Shot returns to Ted, he's finished defrosting, but you see "Low Mileage! 1 Owner" written on the windshield instead. Ted didn't switch cars during the conversation because written on the used car beside the blue wagon is "Like New" for both shots.
Continuity mistake: When Peter and Claude are invisible and walking in New York, just after Claude has released his hold on the T-shirt rack, they bump into a man in a coat. Cut to a different angle, showing the two on camera, and the man in the coat is gone. Instead there are two girls and a man with glasses walking directly behind Peter and Claude, none of whom were there a split second ago. (00:02:05)
Chosen answer: Because he's an idiot. From the story point of view, they needed the vault to actually be physically open so that the release of the virus would be a credible threat. Unfortunately, this required that Peter conveniently forget that he could simply walk through The Wall and use his telekinesis to tear the door open instead. Peter's increasingly large arsenal of abilities, where he ended up having pretty much any ability required for any situation, led to a situation where it became necessary to either have Peter apparently forget that he had a given power, as with the vault door scene, or become naively trusting, as with his refusal to scan Adam's mind to confirm his good intent. This problem, which simply made Peter look increasingly dumb as the show progressed, may well have been a key factor in the decision to severely reduce his ability during season three.