Three. One to climb the ladder while the second kicks the ladder out from under her. And the third to say, "I knew that was too high for you dear."
or
One is a blood-sucking parasite, the other is an insect.
or
I said, "I can't make Tuesdays"
or
Because he wanted to tie the score!
or
They charged one - and let the other one off.
or
He made sure his pools were clean and his lawns were mowed.
or