But Never Surprise Their Bank Accounts!
If you’re going to trigger a cue with a countdown and decide to trigger it early to get a better reaction of surprise, you should be confident your actor(s) can handle the unexpected so you don’t have to reshoot the scene should they break character.
(thanks for the tip, Brian!)
I think in general, I’d be wary about trying to produce a genuine response by startling your actors. Warren Oates chipped a tooth and nearly kicked Ivan Reitman’s ass in Stripes when Reitman decided to go for a “genuine” surprise and have someone knock Oates down during a training exercise scene.
My best “shock” shot so far was in Cult of the Giant Brain and we cycled through that motion repeatedly until everyone was in sync, because in reality, people don’t “surprise” so well.
But it is a technique, I guess…