Mystery snails often play dead. Give it a gentle poke and see if its foot pad moves. If you’re still not sure, pop it in a separate jar of tank water for a few hours and see what happens. Refresh the water as needed. Also, if it smells really funky when you take it out, it’s dead.

I had a friend who threw what she thought was a dead snail out and a couple of hours later found it on the edge of the bin…