Paw Under the Door
My cats think it's such a treat to sneak into the room where I have my computer. When I'm not in the room, I keep the door closed to keep the cats out of the computer room. There are just so many attractive things the cats can play with and so much mischief they can get into while they're in that room. After I've been on the computer, I do a visual sweep around the room to shoo the cats out, but my cats have ways of disappearing by blending in with things in the room: chameleon cats.
I close the door, hoping I got all of them out of the room. It may be hours later, but I will notice a paw sticking out from under the door. They usually don't meow. They just stick out that paw. Sometimes another cat with start playing with that paw, and then finally I realize a cat is still in the room.
This happens over and over again. I guess I should count myself lucky that none of them have had an "accident." Usually the room is none the worse for the incident. They just take such delight in running into any room that is usually closed off to them.