Knife

He couldn't recall exactly when it had started. He'd had a steak knife by the bed for some reason, probably peeling an orange or something, and he'd thrown it at the wall opposite the foot of the bed. It had stuck in the drywall, the hilt quivering for a moment; then, feeling foolish, he'd gotten it out, wiped the knife clean, and put it away. There was a mark in the wall, and every time he noticed it he meant to patch it, but it wasn't urgent. A couple of months went by.
He noticed there was a second knife mark. He couldn't remember, back in...August? September?...whether he'd thrown the knife once or twice. He could only remember the one time, and he'd remember that kind of thing, wouldn't he? There had only been the one cut in the wall, right? He could only remember one. But there were two now. The second one was smaller than the first, only about a quarter inch long, about four inches from the first one. Maybe he just hadn't noticed. He shrugged.
Two weeks later he saw a third mark. This one was horizontal, nine inches below the first one and a little to the left. It had definitely not been there before, and it was deeper than the others. Three days later, there were two more. New ones started appearing every day. They were all in a rectangle twenty six inches wide by twenty nine inches high, as if there was a picture frame on the wall and all had to be inside. They were opposite the foot of the left side of the bed, just where they'd be if someone were sitting up in bed and threw a knife.

He started waking up to find drywall dust on his hands, and in his mouth.
He bought a piece of sheet steel, thirty inches square. He drilled holes in two corners and nailed the steel sheet to the wall over the marks.

The next morning, the nails were on the floor, there were more marks on the wall, there was sand in the bed. The sand looked like ordinary beach sand, except the nearest beach was over 150 miles away. The steel was gone; he never found it. He started sleeping on the couch downstairs; the marks still appeared on the bedroom wall.