"Sesame Street" (1969)
Originally, the character of Snuffleupagus only ever interacted with
Big Bird. He'd always come and go when no one else was around, and
consequently no one ever believed Big Bird when he told them of his
existence. The producers decided to reveal him to the other
characters partially because they felt it was sending a bad message
to children that adults will not believe them if they have something
important to tell them.
Originally, the intention was that the Muppets and the human actors
should be kept strictly separate in different sequences. However,
the producers learned that the audiences were focusing their
attention on the Muppets and ignoring the actors. In response, they
had the actors and Muppets begin to interact in new scenes and
created special Muppets primarily designed for actors to work with,
namely Big Bird and Oscar the Grouch.
