From a transcript of Santorum's interview with the Associated Press:

SANTORUM: Every society in the history of man has upheld the institution of marriage as a bond between a man and a woman. Why? Because society is based on one thing: that society is based on the future of the society. And that's what? Children. Monogamous relationships. In every society, the definition of marriage has not ever to my knowledge included homosexuality. That's not to pick on homosexuality. It's not, you know, man on child, man on dog, or whatever the case may be. It is one thing. And when you destroy that you have a dramatic impact on the quality -

AP: I'm sorry, I didn't think I was going to talk about "man on dog" with a United States senator, it's sort of freaking me out.