Short and sweet:
During Rüffhousin', John goes to hit Norbert's leg. Sound cue fires off early, getting a bit of a giggle from the audience. Actors continue on like normal.
John then runs off the stage for his big "whammo" shot. As he comes down for the mega-hit, the stick flies out of his hand and bounces down the front of the stage. By that point, momentum's got him going through the hitting motion, and he does a great follow-through... sans stick. The sound cue, of course, fires off perfectly.
Audience goes crazy; John, Norbert and Sherie are trying not to break character, but you can see that it's quite hillarious.
John gets the stick back, and whaps Norbert for good measure. Show continues. Story ends.
Girl: If I hear another show tune out of context I think I'm going to vomit. Physically vomit. You know that feeling? --42nd, between 9th & 10th