Sheldon: No, I don't want to go to sleep. You can't make me.
Penny: You're right, we can't.
Sheldon: Yeah, darn straight, you can't. Try to tell a grown man to go to sleep.
Penny: [sings] Soft kitty, warm kitty.
Leonard: [sings] Little ball of fur.
Sheldon: That's not gonna work.
Penny: Happy kitty, sleepy kitty.
Leonard & Penny: Purr, purr, purr.