Revealing mistake: During the fight scene at the end when Buffy is fighting the demons you see her throw one of the demons off the platform. If you watch him fall you can see him land safely on a conveniently placed mat. (00:38:10)
Revelations - S5-E22
Revealing mistake: Just before Teal'c and O'Neill get to the engine room door, Carter can be seen hiding around the corner. (00:27:40)
Revealing mistake: The footage of Monkey Bulk doing flips is just one backflip forwarded and reversed several times - as evident by the movements of the people behind them.
Demon Suite Murder Case: File 2 - S1-E17
Revealing mistake: When Kindaichi looks the name up in the French dictionary, the pages are entirely made up of the same paragraph repeated over and over. (00:08:50)