Continuity mistake: When Jason and his wife are trying to escape from Marwan, they run through a corridor filled with water puddles. A few seconds later, one of Marwan's men goes through the same corridor to follow them, but none of the puddles had any ripples, which they should have considering the amount of water and time elapsed.
Continuity mistake: Day Four: 12:00 PM - 1:00 PM. When Tariq and Behrooz are shown in split-screen digging Debbie's grave right after the commercial break (12:54:10 by the show's clock), Tariq's white t-shirt is covered in dirt. When the shot goes back to them a minute or so later, Tariq's t-shirt is much cleaner.
Continuity mistake: In the first scene where we see Tony as a hostage, Mandy comes over to him and he has a white gag in his mouth, which is taut. Mandy says, "Is she gonna do the same for you?" and the camera cuts back to Tony, whose gag is now limp on both sides.
Continuity mistake: When James phones Jack, who is at Tony's house with Audrey, Jack says they are at "21408, Kipling, North Hollywood". Later, when Secret Service arrives to pick up Audrey, Jack walks outside the house, where we see the house number is actually 21048. The same can be seen earlier when Tony, Audrey and Jack first arrive at the house, but not as close-up. (00:25:05 - 00:30:05)
Continuity mistake: Chloe tells Michelle that she's confirmed Marwan's identity using voice tags from McLennan Forrester, but all of the computer records at MF were wiped out a few episodes earlier by the EMP, according to both the MF employees and CTU. The fact that they didn't get any information from the company except for the printouts Jack and Paul extracted was a major plot point a few hours ago, so even if a real EMP wouldn't do this, the fact that it's stated repeatedly in the show means it should hold true within the series; Chloe suddenly having information from them an hour or so later is discontinuous, and thus a mistake.
Continuity mistake: When Agent Lobell tries to stop a car from leaving the train station, the terrorist in the car shoots at him through a window, shattering it. When the camera cuts to a shot of Lobell falling to the ground, the window in the car is gone, but no fragments of it are on the car or the ground under it.
Continuity mistake: In the previous episode, when Jack and Tony try to stop the helicopter, they drive off the road and hit the front bumper and lose their front license plate. This is also visible in this episode as Jack and Tony wait for backup and when they drive off there is still no license plate, but about 8 minutes later, when they arrive, the license plate is back on. Since the show is in real time and they arrived in the exact time they said they would, they couldn't have stopped to get it fixed or anything.
Continuity mistake: At the very end of Episode 18, Jack knocks out Joe Prado after breaking his thumb and getting information from him. At the very beginning of Episode 19, we see Prado already being treated for his injuries, with a hand splint, and nurses checking his head, within the CTU clinic. Even if you factor in the opening recap sequence at the beginning of every episode, that means that Joe Prado regained consciousness, Jack unhooked his handcuffs, and dragged him back to CTU in three minutes or less.
Continuity mistake: When Curtis Manning is chasing Mary-Ann Taylor out of CTU, you see Mary-Ann exiting through a solid grey door marked by an EXIT sign in a wall which looks like concrete. As she passes through the door, you can see sunlight on her from almost directly above. In the next shot Mary-Ann is seen exiting through a glass door in a wall of glass panels. Unless there is a section of CTU's roof missing, the room she exits from in the second shot is not the room she exits to a few seconds earlier in the first shot.