What does the joke told by Huo Simiao in the 23rd episode of TV series "Mind" mean?

This is a cold joke. Every Sunday at noon 12, several critically ill patients will die in the intensive care unit. It's been like this for a long time. It's scary. Everyone thinks it's strange. Someone was called to exorcise ghosts and hide behind the curtain in the intensive care unit. Then at noon 12, they saw a cleaner come in to clean up. The cleaner skillfully mopped the floor, saw the breathing plug connected by the critically ill patient in front of him, skillfully unplugged it, and then plugged it in after mopping the floor. ...