The classic way to tell if someone was a witch was to tie them up and throw them in water. If they lived, then it was because the water rejected those in league with Satan, so the accused was a witch and would be executed. If the accused drowned, it proved they were innocent. (At least, this is how the story goes when maximising the ridiculous irony. In actual practice the accused would be rescued before they could actually die of drowning. Sometimes.)

You can adapt this technique to all sorts of roleplaying situations. It's a great justification for "shoot first, ask questions later". See? All sorts of realistic roleplaying situations that occur many times in actual games.

Transcript

Leia: Han, Chewie, get out there and investigate.
Han: I was just out there! It's cold.
Chewbacca: Stiff upper lip, old chap.
Han: That's what I'm complaining about!
{scene change, snow}
Han: All right then, here's the plan. We see what the droid wants. If it's hostile, we destroy it.
Luke: How will you tell if it's hostile?
Han: If it shoots back.
Luke: Jim, focus, please, for goodness' sake.
Han: What do you mean, Corey?
Luke: Look, sorry, but your plans are getting dumber by the minute.
Han: Thanks!
R2-D2: Wait. Jim, do you know what "non compos mentis" means?
Han: "Not of sound mind", i.e. not mentally competent to stand trial.
Han: A bit of an exaggeration for Han, but pretty close.
Luke: You mean you're deliberately playing Han as stupid?
Han: You couldn't tell?