Early in the movie Doc Holliday (Kirk Douglas) goes into a bar to confront a bad guy. Doc stands at the bar and watches the bad guy through the over-the-bar mirror. When the bad guy draws his gun Doc quickly turns and appears to draw a switchblade from behind his neck, which he throws at the bad guy, killing him.

Watch Doc's right hand, which is on the edge of the bar, as Doc is looking in the mirror. You can see that he picks up the switchblade that has been hidden there. When he quickly turns, he goes through the motions of drawing the knife from behind his neck - but it's already in his hand!