Duck's Unusual Greeting

Listen here, buddy. This joke is all about wordplay. You see, the duck wants the butt to "smell good." But "smell good" sounds like "smell good", as in, the duck wants to sniff the butt. It's funny because ducks don't usually go around sniffing butts, and it's unexpected. It's kind of like you trying to understand advanced physics – unexpected and probably not gonna happen.