Just in the Halloween night, I need to catch up with the company business, so I work until 12 o’clock to deal with all things. I wanted to go home and get a good night’s sleep, so I immediately went to the elevator to leave the company building. Corridors are exceptionally quiet at night, because at this time, the only people left in the building are the guards in the janitor’s room. But just then I noticed the sound of footsteps on the corridors behind me. I was a little scared because my company was the only company on this floor, and now I was the only one working currently. Luckily, the elevator in front of me has arrived. I hurry to get into the elevator and press down the first-floor button. As the elevator doors closed, I began to feel safe. Suddenly, on the way down, the elevator door in front of me had a clapping sound. I stand back and against the wall behind me. The clapping became louder and more intense. I always felt unusual things would come out of the elevator door in front of me. At that moment, however, the elevator reached the first floor and the door opened behind me. I quickly get into the elevator door and away from the clapping in front of me. But outside the elevator, the building was dark and devoid of light, including the janitor’s room, which is normally lighted 24 hours a day. And then All of a sudden I remember: the elevator in the building only has one door, but I just stared at the elevator door and walked out, which door did I walk out of?