I think she's the only one who can pull that off

(following a conversation about various ways in which a student who wanted to do so might become pregnant)

Student 1: Not in vitro fertilization. I can't do that. I'm Catholic. It's a sin.
Student 2: You're single. How are any of the other things we've discussed not a sin?
Student 3: You can try to be sinless; it worked for Mary.

Overheard in: commuter lounge