Lost actor Matthew Fox was stabbed for real while filming the series

“We had a fake knife and a real knife,” Bender told the outlet more than a decade after the series finale aired. “The real knife, like every time you make a movie, is dull. But it's a real blade so it doesn't wobble, because all rubber blades do that a little bit.” The director directed 43 episodes from the first to the last season of the series and was also executive produced. So he undoubtedly had a lot of experience in how prop weapons were handled on set, as did O'Quinn at that time. Bender noted that “Terry worked with a real knife and a fake knife”, using both to make the fight sequence as real as possible.

From the sounds of it, the real knife was likely used for shots in which it would be more visible, while the rubber prop should have been used for moments of real impact between the actors. “Terry had learned well to have the real knife in his hand, even if it was dull, and when he would drop it and right next to him, inches away would be the fake knife,” Bender said. Except that's not what happened during a nerve-wracking moment at the end of filming, when O'Quinn accidentally grabbed the real knife instead of the prop. The actor remembers getting caught up in the action of the moment, which involved grappling and apparently also featured fire hoses on set to simulate a storm.