Jiang Chen, a junior student in the Department of Computer Science at Jiangcheng University, registered as a part-time rider on the "Qida" food delivery platform in order to collect tuition for the next semester. He thought it was just an ordinary manual job, until one rainy night, he took a takeaway order to Tongzilou in the old city. The person who opened the door was a middle-aged man with a bandaged arm and eyes like a hawk. The man did not take the takeaway, but stared at Jiang Chen for three seconds, and then said: "Boy, it took you forty-seven seconds to go upstairs, but your heartbeat only accelerated twelve times - have you practiced?"
