Just one, but he'll also want to do something about your nose.
or
One is a blood-sucking parasite, the other is an insect.
or
They are both rolling in the dough!
or
Anything you like, he can't hear you.
or
Only one, but it may take upwards of five years for him to get it done.
or
The letter H.
or
Does Boston stop at this train?
or