I'm guessing everybody already knows this. But a good exercise for crabs when you're sitting (or standing) around doing nothing, is to make an audible finger snap with all four fingers individually. Either on both hands at the same time, or alternating from one hand to the other. Try to increase the speed until you mess up, then start over & do it again.
I think a good time to do it is when you're watching TV by yourself.
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