All you need to engender terror is the creeping unknown. What are the things behind what are usually mundane. In this case, a terrified woman lives in a mental hospital, fearing that there is something in walls where patterns exist that could lead to her demise. Enter a young new director who takes her under his wing, but she lies to him and so he is helpless to do much of anything. This is one of the more creative of the middle Twilight Zone shows. It will make one think twice as we lie in bed, staring at the wall. There is a classic ghost story that certainly lays the foundation for this particular episode.