Probably about 20 years ago someone told me about a minor blooper that made it past editing and into the show. To the best of my recollection- McCoy is standing near two characters having a conversation (I assume Kirk and Spock.) He's holding some sort of little doohickey, and he accidentally drops it. He looks around and sees that nobody seemed to notice, then reaches down and picks it up. I recently bought the OS on blu-ray and got a few episodes into season 3 before I remembered I wanted to look for this. Anyone know which episode it's from? Thanks.
I think you're thinking about the scene in "Space Seed" when Shatner's communicator falls off while he's busting open Khan's cell with his phaser. Wow, that's a mouthful.
I think you're thinking of "Space Seed" when Kirk's phaser drops off his belt while freeing Khan from the sleep chamber. De Kelley noticed that it fell and he keeps looking at it, finally bending to grab the prop. EDIT: Yeah, what Esteban said...as I was writing mine.