Johnny the Homicidal Maniac Easter Egg - Little Shop of Horrors

Go to the part where Tess is talking to Johnny. She finds out that he is killing people to feed his wall. The the last frame of that page (Tess notices he is quoting the Fly), the wall is saying, "Feed me Seymour"

This is a reference to Little Shop of Horrors. Seymour has a carnivorous plant that requires blood to survive. Very appropriate for Johnny's wall.