Episode 3833

Season 30

Telly Monster keeps seeing a letter X with weird-looking eyes appear and then disappear, but, much like how everybody used to think that Mr. Snuffleupagus was Big Bird's imaginary friend, nobody believes Telly whenever he tells them about the strange-looking X, and it's never around when they are looking. Eventually, the others do see the X, and the X turns out to just be a normal X, and explains that his weird eyes are actually sunglasses.