Attention evil GMs

Something reminded me of a wonderfully pervertible bit of geology.

Have a large courtyard with a gong and striker hanging there. The courtyard is unpaved just surfaced with some sort of damp clayish stuff.

if the gong is struck it produces *much* stronger (and deeper) vibrations than you'd expect. The vibrations cause the thixotropic clay to temporarily liquefy. Better hope bedrock isn't to far down!

This could also work in an underground chamber.

If you want to be more fair, have a sign in a language *not "common tongue that says "do not strike gong"