One of them was known as Sister Mathematical (SM), and the other one was known as Sister Logical (SL).
SM: Have you noticed that a man has been following us for the past thirty-eight and a half minutes? I wonder what he wants.
SL: The only logical thing we can do is split. You go that way and I'll go this way. He cannot follow us both.
Sister Mathematical arrives at the convent and is worried about what has happened to Sister Logical.
Then Sister Logical arrives.
SM: Sister Logical! Thank God you are here! Tell me what happened!
SL: The only logical thing happened. The man couldn't follow us both, so he followed me
SM: Yes, yes! But what happened then?
SL: The only logical thing happened. I started to run as fast as I could and he started to run as fast as he could.
SL : The only logical thing happened. He reached me.
SM : Oh, dear! What did you do?
SL : The only logical thing to do. I lifted my dress up.
SM : Oh, Sister! What did the man do?
SL: The only logical thing to do. He pulled down his pants.
SM: Oh, no! What happened then?
SL : Isn't it logical, Sister? A nun with her dress up can run faster than a man with his pants down.
And for those of you who thought it would be dirty,
Say two Hail Marys!