I do so love the Yip Yips.
Edited to say: BTW, PBS isn't responsible for Sesame Street's content. That would be Sesame Workshop (formerly Children's Televison Workshop). They also made The Electric Company, 3-2-1 Contact, Square One, and a LOT of other shows that PBS airs, however. They're really dropping the ball with Sesame Street, though.
If only Jim Henson were still around.