Mean Mama's Baby

From Muppet Wiki

Mean Mama's Baby is small, brown, one-toothed furball that made its only appearance in the "Beast of the Week" sketch on episode 201 of The Muppet Show.

In the sketch, Don Knotts introduces the baby to the audience as a new creature which has just been discovered. Although he is unfamiliar with its behavior, Knotts proceeds with his demonstration, only to find that the creature can contort itself through "inescapable" holding bars.

After a brief period of interaction with Knotts, the creature calls for its mother, who arrives to "save" her baby, scaring Knotts right out of the sketch.