Peanut, nude as usual, and suddenly standing next to me: Mom, why is my penis stretching out?
Me, glancing right, gasping in terror, then rolling my eyes: Because you have a boner, son.
Peanut: What's a boner?
Me: When your penis get hard.
Peanut: Gets hard?
Me: You know. When it stretches out.
Peanut: Oh. I thought it was stretching because it's tired.