An alien couple beam themselves down to Earth and get chatting about their contrasting experiences of life with an Earthling couple that they meet: Linda and Keith. Soon enough, the conversation turns to sex, and they decide that it would be an immensely useful one-time interplanetary scientific experiment for them to swap spouses for the night and gain lots of valuable data from the liaisons that could be used for future transformational research.
Linda and the alien man go off to a private room together and get undressed. She's absolutely crestfallen to see that his willy is really, really tiny; but he tells her not to worry - this is just 'efficient everyday mode'. He puts his hand on his ears, twists them sharply, and to her delight, his willy quickly grows to the size and girth of a rounders bat.
They have a very wild time - at it the entire night in all kinds of positions and scenarios, with both of them screeching nonstop with delight. When the morning comes, they're both still buzzing with excitement and can hardly believe what happened.
They bid each other farewell and return to their respective spouses. Linda says to Keith, "Wow, that was an incredible experience. He taught me so many amazing things, and I taught him so much too. What a fantastic night of pure pleasure! I will never, ever forget that as long as I live - without doubt one of the very best experiences of my entire life! Go on, Keith, tell me what it was like for you with Mrs Alien - I'll bet you're still throbbing with unforgettable immense ecstasy, aren't you?!"
Keith just stares at her as though she must be utterly mad and says "What on earth are you talking about, Linda? How could you possibly have enjoyed that? Alien sex is without doubt the most boring, weird, unsexy non-experience ever, and I was so glad when it was finally over. She just spent the entire night frowning at me and constantly trying to pull my ears off!"