The other weekend (on Mother's Day, actually) I had the privilege of seeing Bill Cosby live in concert. It was a great show, and the audience was literally roaring for most of it. But one thing stood out for me -- Cosby's interaction with the lady translating the act into American Sign Language on the fly. At various points in the act, Cosby would apologize to the translator, then head into what seemed like an untranslatable bit (for example, the "dentist" bit below -- when he gets into the "numb mouth" part). But the translator was absolutely up to the task -- from what I would tell (knowing zero sign language myself) she switched into using the American Manual Alphabet at various points, spelling out words with furious speed, and mixing the spelled-out bits with full-word signs. At the end of the dentist bit, the audience cheered -- for the translator!
Here's the bit in question (though from a performance 24 years ago):
Further reading: Wikipedia on American Sign Language.