A bizarre NetHack tool that would be entirely useless except that you can apply it once per turn at no time cost; that is, it doesn't count as your action for that turn. Applying it more than once per turn will cost you one turn per use. The stethoscope will sometimes probe adjacent monsters, showing their hit point totals, etc, and will also find secret passages. A cursed stethoscope has a 50% chance of just hearing your own heartbeat. The whole thing is pretty sketchy -- I'd keep your distance from a NetHack player who regularly uses a stethoscope.

Applying a stethoscope produces some funny messages in certain situations:

Applying to a corpse, when hallucinating:
"You hear a voice say, "It's dead, Jim."

Applying to a statue:
"The grid bug seems to be in excellent health for a statue."

Trying to apply it to an invalid location:
"You hear a faint typing noise."