I've done my share of singing, choral and solo, sacred and secular and silly. This, however, takes the cake.
It's actually very difficult to sing properly while cracking up. What separates the pros from the wannabes is keeping a straight face and sticking to the script when it's obvious that you're going over big with making the audience laugh. That little half-smile represents a serious effort of will. I got this from John Scalzi.
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