Спільний звук

Rohan was alone in his room at night. His phone suddenly vibrated. A message from an unknown number appeared. It said: "I'm behind you." Rohan laughed and replied, "Nice joke." Then another message came. "Don't turn around." Rohan's heart started beating fast. Slowly... he turned his head. No one was there. Relieved, he looked back at his phone. A final message popped up. "Too late." And suddenly… The lights went out.[sarcastic]