Revealing mistake: John Kramer's chain first goes on the side of his stomach, and then it's on his backside... impossible, otherwise the chain would split him. (01:35:47)
Revealing mistake: When Jason is getting stabbed to death, there's a quick 2-second shot showing him being stabbed repeatedly in the stomach, with part of his intestines hanging out. But if you pay close attention, there's no actual damage occurring with any of the stabs, revealing it's just an effect. Likely either a collapsible prop knife or a CGI knife being stabbed into him.