One Friday evening the party girl headed out for night on the town, and asked her flatmate to come along.
The girl declined and said she was going to read and then go to bed early.
The girl had been out at the local bar for a few hours when she remembered she had forgotton something.
By this time, pretty plastered, she stumbled back to the appartment and quietly let herself in. Not wanting to wake her flatmate, she didn't turn the light on, picked up whatever it was she went back for and returned to the bar.
When she got home the next morning, she opened the door to this:
Her flatmate's head had been cut off and was lying on the floor.
Scrawled in her blood on the walls were the words "Aren't you glad you didn't turn on the light?"