Initially, it was assumed that the voice was a woman's voice. Officers brought in a drone to scan and found traces that looked like a human body. Then, from the front, they brought a sonar device, which is a device for detecting objects by detecting sound signals, down under the hole and shouted that if there were survivors in the area, they should knock to confirm their position, which the officers felt as if they heard a knocking sound in response.
credit : สล็อต