Mr. Moose was a puppet character on the children's television show Captain Kangaroo.
He would tell riddles and knock-knock jokes that would result in hundreds of ping pong balls falling from above, and hitting the Captain on the head. Mr. Moose was created and played by Cosmo Allegretti, who also created and played Mr. Bunny Rabbit, Dancing Bear, and the Captain's painter and handyman Dennis.
In the animated television series Family Guy episode "Hell Comes to Quahog", after Joe sends a ping pong ball out a window, Peter persuades Mr. Moose to say "Knock, knock", then answers "Ping pong balls!", and ping pongs balls fall on top of Peter.