Kitty goes bonk.
So last night I was downstairs in the kitchen making myself a cup of tea, and the cat was doing his almost-nightly Run-Around-Like-A-Mad-Kitty-For-No- Obviously-Discernible-Reason thing and the door to the room where his litter box is was slightly open, and it's a bathroom so there's a sink in that room. He ran full speed to the open door, leapt--presumably to leap ONTO the sink--miscalculated the height, I guess, and crashed full-force, face-first, into the side of the basin. He's fine now, he was just a little startled for a few moments. It was hilarious, though.