I thought it was closer to uterus, and that’s what he was thinking of? A kid that age would be more likely to know that word because of health classes; they don’t teach words like ‘vulva’ (in the US, at least. Too sexual, I guess 🙄) which is why so many people don’t learn there’s a separate word for vulva and vagina until they’re way older.

Either way, though, I too always think of this joke!