U is for under.
Sometimes, kitties like to hide under things.
When a storm comes, some cats like to hide under a bed. Sometimes, cats in strange bedrooms like to hide under the bed. Sometimes we hide under the couch or other furniture. Sometimes we go under, but we aren't really hiding.
Sometimes on a hot day, we hide under something to keep cool.
Queens who are about to have kittens often try to hide under something. When Smudge had her litter with Friendly, Dark Lady, Sir Ed, and Pretty Grey Lady, she hid under the shelves to have the kittens. Mama Kitty had Truffles and that litter under some scrap metal out back. Rico was looking for a place to hide her kittens when she had kittens in our last spring in the shed. This usually keeps the predators from getting to the kittens even when they find them.
When it rains, we like to get under something to keep the rain off.
And if a door is closed, we try to see if we can get under the door. Usually we can only get a paw through the door.
But if your humans park their car where there might be cats, the cats sometimes crawl up under the hood. Or under a truck.
And on laundry day, we sometimes like to sit on our humans' underwear.