|Harvey Kneeslapper and his frequent victim, Mr. Johnson, on Sesame Street.|
Most of us know what to do in case of a knock knock joke. If you're not the one telling the joke, your responsibility is clear. You have two lines, both questions: "Who's there?" and "________ who?" Those are easy enough to remember. But what happens if the joke itself is in the form of a question? Are you supposed to actually answer it in an intelligent fashion, like you've really put some thought into, let's say, how many Christian Scientists it takes to change a light bulb? The answer is no.
Most likely, the joke teller just wants you to say, "I don't know." Practice saying that with me. I don't know. Good. If you really want to participate in the joke-telling process, you can say, "I don't know" and then repeat the original question, often with an emphasis on the second word. An example: "I don't know. What do you get when you cross a goat and an owl?" And then the joke-teller will tell you the punchline. That's how jokes work.
Don't try to guess at the answer. You're just wasting further time and making an already unpleasant experience worse. In fact, don't even bother with the "repeating the question" thing. Just say, "I don't know." Follow these simple guidelines, and you, too, can be an effective joke recipient.
By the way, it takes one Christian Scientist to change a light bulb. He just prays for the old bulb to start working again. And the unlikely crossbreeding of an owl and a goat would yield a hootenanny.