Speleothems

Speleothems are cave formations that can be produced in the form of stalactites and stalagmites. A set of both were seen in a sketch from episode 307 of The Muppet Show in which they complain about a toothache ad the fact that they hear voices. The sketch ends showing that the first set of speleothems were in fact the teeth of the second set revealing an example of infinite regression.

In episode 108 of Muppets Tonight, a set of four stalactites can be seen on the set of Jason Alexander and Gonzo the Great's closing number, "Bats: the Musical."