Re: The Thing (1982)
I saw this in the cinema when it was first released.
My brother, a real wiseguy, went to see it a second time and made sure to sit down right next to someone he didn't know. (The cinemas were rarely packed, and people tended to spread around.) He waited until that scene when everyone is tied to the sofa and MacReady is testing blood samples with a hot wire.
Mac finds an infected person, and the guy immediately begins to shape-shift: twitching and quivering. At the same moment, my brother also started twitching and quivering. He really freaked out the guy next to him.