Not bursting, informing. :-) The idea is more that they're being taught the specific choreography which will be performed at the end of the play, so even if some of the characters are familiar with the steps they can still reasonably be subjected to this one session so that they can then practice this particular sequence on their own and be 'fluent', as it were, once the performance rolls around. And, really, the focus is John and Sherlock. Everyone else is just along for the ride so some of them being somewhat experienced would actually be a plus (I bet Molly is going to know what she's doing.). Of course, at least one of them is going to have to prove completely clueless for comedic effect.

Lots of youtubing and googling going on. :-)