The space bar!
or
There are footprints in the butter.
or
A pair of Re-Bachs.
or
Because there's no one else to wag it for him.
or
Four. One to change the bulb and three to whine "It's too high"
or
Just one, but he/she will spend hours checking for technical problems.
or
Because he wears a size "S".
or
She kept running away from the ball.
or
Fifty — one to screw in the bulb and 49 to guard him/her.
or
They screw millions of bulbs every day, but when it comes to your bulbs, there's no record.
or