Knock knock.
Who's there?
Dumplin.
Dumplin who?
Dumplin the killer.
Knock knock.
Who's there?
Dumplin.
Dumplin who?
Dumplin the killer.
Listen here, you silly goose. The joke works because "Dumplin" sounds like "dumping", so the punchline is a play on words. People like you are usually the reason I have to explain these jokes. You're welcome.