In The Restaurant at the end of the Universe, Douglas Adams envisaged a genetically engineered cow that was intelligent enough to tell the restaurant-goers that it wanted to be eaten.
“You mean this animal actually wants us to eat it?” whispered Trillian to Ford.
“Me?” said Ford, with a glazed look in his eyes, “I don't mean anything.”
“That's absolutely horrible,” exclaimed Arthur, “the most revolting thing I've ever heard.”
“What's the problem Earthman?” said Zaphod, now transferring his attention to the animal's enormous rump.
“I just don't want to eat an animal that's standing here inviting me to,” said Arthur, “it's heartless.”
“Better than eating an animal that doesn't want to be eaten,” said Zaphod.
“That's not the point,” Arthur protested. Then he thought about it for a moment. “Alright,” he said, ``maybe it is the point. I don't care, I'm not going to think about it now. I'll just ... er ...”