Two American astronauts are launched to Mars.

Two American astronauts are launched to Mars. When they reach the Martian surface they see a beautiful red-skinned, red-haired woman. Using their language-translation machine, they tell her they are from Earth. They see she is stirring a big pot, and every now and then she pulls a newborn baby from the pot. So they ask her, “What are you doing?” She replies, “Making babies,” and she continues to stir. “How strange,” the astronaut commander says. “Well,” the beautiful woman asks, “how do you make babies on Earth?” So the commander says, “Let me show you,” and they go behind the Martian rocks and bushes. After a while, they come back out and woman asks, “Well, where is the baby?” And the commander says, “Oh, back on Earth it takes nine months to have the baby.” Perplexed, she asks, “Then why did you stop stirring?”

This joke was Wernher von Braun's favorite.