Jeff Chase is an actor and stuntman who has been in the business consistently for years and is well respected, though not well known. He was shooting a scene for Dexter, the awesome Showtime show about a killer who kills killers.
In this scene, Chase was supposed to get stabbed by Jimmy Smits using a prop knife, but somehow, Smits got his hands on a real knife, claims we was completely unaware it was real, and stabbed Jeff Chase multiple times in the chest. In front of tons of people. And on film.
The weirdest part is Smits went into a sort of stabbing-trance, and just kept stabbing Chase, until Michael C. Hall (aka Dexter) yelled STOP at him multiple times.
Chase survived, and so did the other five actors in this post from Unreality magazine. Link