I guess what's really great is when something happens, and there's a technical difficulty, the Muppeteers will improvise something.
Take for instance X-mas on SS... At one point Ernie's trying to open Bert's present. Jim (and whoever was working the other hand) had a tough time trying to open it, to which Frank Oz adlib'ed Bert's line "Wrapped it good, didn't I?"
I guess that's what happened with "Honk Around the Clock" as well.
I can note several times where large crumbs are visable on tables after Cookie Monster feasts, and Frank will add "Come here you" or something to that extent. One time a huge Crumb was visable in his mouth, Frank promptly puts cookie's finger into the mouth and pops it out adlibbing "Need toothpick..."
Another such example falls into Count it Higher (which I posted numerous times before). The three AM's singing was out of continuity, so at some points one mouths the singing while the other is supposed to. At one point, two open there mouths at the same time, though only one person is singing. However, the Puppeteer (Mayhaps Jerry nelson) of the Smaller AM, improvises a bit where the littler one looks in shock as the other sings his line. On the second time around counting to 10, the smaller AM looks at the one who previosuly stepped on his line in anticipation of his singing...