Nothing, it shuts them up!
or
Weeeeeeeeeeeeeeeeeeeeeeeeeee
or
Woke up in the fireplace.
or
Just one, but he/she will spend hours checking for technical problems.
or
Seven. One to change it and the other six to sing about how good the old one was.
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Anything you like, he can't hear you.
or
A snail because it carries it's home.
or