Imagine if you will, The Welsh National Coal Board Choir.
They are all dressed in their finest suits and wearing Dickie Bows.
The conductor taps his baton on the music stand and calls the choir to order.
They just begin the very first notes of the ancient seamans hymn "What shall we do with a drunken sailor", when, all of a sudden, and quite unexpected, the floor of the stage drops to one side and the entire audience throw buckets of freezing cold water at them.
Now that, dear friends, is a "hitch" !
Slightly difficult to reproduce in your average folk club, eh ?