Pointless
or
One; she designs the bulb to crawl up the wall, unscrew the old one, and screw itself in.
or
Three: One to screw it in, and the other two to help him down off the keg.
or
They stamp their feet.
or
Because they don't fit on a ironing board
or
The bartender offers him a warm smile and says, "For you, no charge".
or