The Truth Is Out There - S1-E17
Revealing mistake: Gibbs finds a bunch of cash hidden in the victim's speaker. "For Motion Picture Use Only" is printed on them.
Revealing mistake: After the Custos's house has been broken into, the next day, the Custos takes a key out of his jacket pocket, unlocks a drawer and takes out a pile of bound papers. When he closes the drawer, he doesn't take the key out of the lock, but he pantomimes his hand returning the key to his pocket.
Revealing mistake: When Mr. Hathaway contacts Scotty as they dig up his son's bicycle, a shot of Hathaway shows Los Angeles' US Bank Tower in the background. The series is set in Philadelphia.
Revealing mistake: In brother Justin's padded cell, the far wall is obviously a painted backdrop. It even flutters when the orderly and doctor walk in! The only solid part is a couple of feet at the end, that Justin leans up against.
Revealing mistake: When Jamie sits down after rappelling down the canyon wall you can see that he has climbing rope attached to his harness. It's wrapped in duct tape to look like its the rope he and Adam made of duct tape. This may just be a safety line to support his weight if he duct tape rope snaps, but the Mythbusters usually point out any backup safety systems and explain that they are there for caution and don't contribute to the test. (This was explained in the aftershow. It was a safety line required by the shows insurers).