Jaw clenching caused as a side-effect of consuming LSD. Generally not dangerous. Treated by staying hydrated and exercising the mouth. Nothing to worry about as worrying can cause a bad trip.
Luke: You just gotta watch out for The Clench
A.J. (On LSD): The Clench? Wtf is that?
Luke: You don't know about The Clench man? That shit will lock your mouth shut!
When a human dies, their final instinct is to clench their lower orifices. This is why Necrophiliacs claim that corpses are better than the real thing.
Human 1: Dude you see that girl when she was almost stabbed.
Human 2: Yeah, you could see the clench instinct kick in.
Human 1: Yeah dude, it was hot.
Stephen Hawking: My best discovery for science was and will always be, the clench instinct.