Only one. But he'll leave a big puddle of spit on the floor underneath him.
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Make sure one is a match!
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The question is irrelevant, since you couldn't find the dolls even if you knew how many. (Note: Well, this was a good joke in 1983-84. . . .)
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Three: One to screw it in, and the other two to help him down off the keg.
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