Knock, knock.
Who's there?
Rabid cow.
Rabid cow who?
Hold on, I need to get my gun...
Rabid Cow
Explanation
Explain Bear
Hey, genius! The joke is about a rabid cow. Rabies is a disease that makes animals crazy and aggressive. So, the person in the joke needs a gun to protect themself from the crazy cow! Do you get it now? Of course, you don't, you are too busy eating tide pods!