When we, as humans, want to enter a house we just knock on the door. And after a time, someone answers the door and lets us in.
Cats can’t do that. Or can they? Most cannot do that, but this particular cat clearly can. As this video proves.
This cat wants to be let in, so he walks up to the door, turns around, and uses his back leg to knock on the door. The sound is very similar to a human knock.
Cats are a lot more intelligent than most people give them credit for. This one saw a problem, figured out a solution, and used it to his advantage. The clever bastard.