'ghosts beating the wall') refers to ghosts trapping people in a certain area at night.
There is a folktale about a traveler who walks in circles, as if ghosts continually built walls to block his intended path.
[3] The conventional solution is to stop, cover one's face with one's hands, then look again to see that the way is clear.
[3] The contemporary Chinese artist Xu Bing referenced this folktale with his artwork Ghosts Pounding the Wall in 1988.
[4] With a crew of workers, he took ink impressions of the Great Wall of China and displayed them in the United States.