Medical School Tragedy

When I returned home from studying abroad, I noticed an 'X' written next to my front door. I didn't pay attention and simply wiped it off. But when I returned home that day, the 'X' reappeared. I thought it might be some kid playing a prank. That night, I was working at home when loud cartoon noises came from the neighbor's apartment. I was too annoyed to work, so I knocked on the neighbor's door to discuss it. The next day, when I left for work, the 'X' on my door had turned into a '0'. Just as I was wondering about it, the neighbor's door suddenly opened, and when I saw the neighbor, I knew danger was coming...

On a dark and stormy night, a couple was speeding in an unfamiliar city. Suddenly, a tire blew out, and they had no spare. So the husband went to find help. He was worried his wife wouldn't be safe in the car, so he locked the doors and windows before leaving and told her not to get out. When he returned, he found his wife in a pool of blood, and there was even a stranger in the car.

You live alone in the countryside, with only one neighbor, a couple who raise cows. There's a lawn between your two houses. One late night, you were woken by a commotion, then heard cow mooing, the sound of a cow breaking through a fence, and a cow eating grass. After some time, you heard something hitting your front door, but you ignored it and went back to sleep. The next day, the police knocked on your door.