Revealing mistake: When Kate Warner phones her sister, Marie holds her phone up to the camera and you can see that the words "KATE'S CELL" have been written using the 'Write Messages' function on her Nokia. The 'abc' in the corner gives it away plus you can see the cursor trying to be hidden by being moved next to the 'K'
Revealing mistake: Right after Kim Bauer and Miguel start a fire in the police van, the vehicle swerves off the road and tumbles. In the next shot, you see "Kim" on top of the car, trying to get in through the window (the car is about to fall off a slope or something). Pay close attention, zoom in, or whatever, the woman is not Kim but is a stunt double. She's got a much chubbier-looking face and is definitely not Kim Bauer. This occurs at 19:40 in this episode.
Revealing mistake: When Michelle is in the van, waiting for the computer to finish analysing the conversation between Alex Hewitt and Sherry Palmer, the computer bleeps to says it has "heard" enough of the conversation to be able to recreate Hewitt's voice. How ever, it bleeps whilst Sherry is in the middle of talking. The computer should have made the noise about 15 seconds before.