Martian Sex

For an experiment on the effects of deep space travel on romantic relationships, NASA sends a married couple to explore Mars.

After the couple lands on Mars they begin exploring the surface. To their surprise they bump into a pair of Martians. The Martians looked just humans, except they're green. And by some method that's irrelevant to the joke they speak English. The astronauts start talking to the Martians about various things, culture, history, etc. until the topic of sex comes up. They discover that Martians have sex just like humans. In the name of science, they decide to swap partners for the evening.

Cut to the human female with the Martian male. The Martian male takes off his pants to reveal a micropenis. The human female says "Wow, that's very small! I don't think this is going to work."

Martian male: "Oh, sorry! Hold on a sec!" He begins slapping himself on the forehead, and each time he slaps himself his penis gets a little longer.

Human female: "Wow, that's impressive! But it's still very thin."

Martian male: "Oh, sorry! Hold on a sec!" He begins pulling on his ears, and every time he pulls on his ears his penis becomes a little wider. Now he's got a real hog, and they go at it.

The next morning, the human couple meet up to recap their night. The human female says "Honey, please don't get upset, but last night was really great for me! How was it for you?"

Human male: "Horrible! My head is killing me! She kept pulling on my ears and slapping me on the forehead all night!"