If you didn't know what sleep was, and you had only seen it in a science fiction movie, you would think it was weird and tell all your friends about the movie you'd seen.
They had these people, you know? And they would walk around all day and be OK? And then, once a day, usually after dark, they would lie down on these special platforms and become unconscious. They would stop functioning almost completely, except deep in their minds they would have adventures and experiences that were completely impossible in real life. As they lay there, completely vulnerable to their enemies, their only movements were to occasionally shift from one position to another; or, if one of the 'mind adventures' got too real, they would sit up and scream and be glad they weren't unconscious anymore. Then they would drink a lot of coffee.
So, next time you see someone sleeping, make believe you're in a science fiction movie. And whisper, 'The creature is regenerating itself.