Cathy from Minnesota offers this joke…
Knock, knock 
Who’s there?
Turnip
Turnip, who?
Turnip the heat, it’s cold in here!
Explanation: This joke plays on words turnip/ turn up. A turnip is a vegetable; “turn up” is what you do to the heat when it is too low (you can also turn up the radio, …).
Q. What runs around a soccer field but doesn’t move?
A: A fence
Explanation: This joke plays on the word “runs”: A person runs; a fence runs around, that is, goes around, an area like a soccer field.
Knock, knock. 
Who’s there?
Lettuce.
Lettuce who?
Lettuce in and you’ll find out!
Explanation: Knock-knock jokes play with words: words that sound the same but are different or words that have more than one meaning. In this joke the jokester is playing with the words “let us” and “lettuce.” It is funny because the listener assumes the word is lettuce.
Q: Why did the chicken cross the road?
A: To get to the other side.
Explanation: The answer to this joke (“To get to the other side”) is so obvious, something everyone knows, that it is funny because it is silly, perhaps even stupid. Why else would you cross a road except to get to the other side?
Explain the Joke 