A monk turns 18 and leaves the monastery for the first time. As he walks down the street, a sex worker says, "Hey, Father! How about a little head? Ten bucks."
Unsure what this means, the young monk hurries back to the monastery. He finds a nun and asks, "Sister, what's 'head?'"
She replies, "Ten bucks—same as downtown."
(Explanation: "Head" refers to oral sex.)