Sheldon and Amy do a scientific evaluation when she gets turned on by Zach. They determine that she's horny. He wants her to go out with Zach, but instead she tries a hand-holding experiment with Sheldon.
Sheldon: Why do you have the Chinese character for "soup" tattooed on your right buttock? Penny: It's not "soup," it's "courage." Sheldon: No it isn't. But I suppose it does take courage to demonstrate that kind of commitment to soup. Penny: How'd you see it? You said you wouldn't look. Sheldon: Sorry. As I told you, the hero always peeks.