Ape, Elephant, or Artist?

I keep missing a comedy gag that is on David Letterman but apparently they show a piece or artwork and then ask the audience if it is "ape, elephant, or artist"! Has anyone seen this??

Ape Or Artist (Letterman and Shaffer are shown a painting and they discuss whether an ape or an artist painted it - always an ape)
Ape or Artist or Elephant (nearly identical to Ape or Artist, except with the possibility that an elephant painted it)