At the end of the Julie Andrews episode, during the goodnight Kermit says that "this has really been a moooo-ving experience", referencing the cow backstage. But for the most part, the cow was only on-stage (the only known instance of the cow on-stage being when The Swedish Chef brings it on his set, but even then, does the audience see this or is the curtain down? I feel the Chef was preparing for his act, the curtain not yet up). So the audience (in the Muppet theater) wouldn't get the joke, unless there were monitors on the set to show them what happens backstage (but then we never see any such things in the Muppet theater).