I heard lots of cackling when Fozzie and Peter were doing their lecture on "post-Dickensian...whatever it is."
But if you really want to hear Richard lose it, watch the episode with Valerie Harper, and stay alert during the Swedish Chef skit (the one with the Japanese cake). You can hear him loud and clear, and as an added bonus, for a split second by the Chef's left elbow, you can see the top of Richard's head.