Sheldon: Oh, come on, you can't tell me that you're not intrigued about the possibility of building a better girlfriend.
Leonard: I'm not. And Penny's qualities, both good and bad, are what make her who she is.
Sheldon: You mean, like that high-pitched, irritating laugh?
Sheldon You wouldn't prefer a throaty chuckle?
Leonard: You're not changing how Penny laughs.
Sheldon: No, that would be incongruous, I was going to lower the whole voice to a more pleasing register.