In a storage building near the highway, near the back, Eddie Decae rents a small space for the storage of a single object too disquieting even for his shop: A small square of wood taken from a downtown ballroom during the twenties. The wood was originally part of a dance floor, but it was ruined by a splatter of blood that struck it during a violent murder. The blood is perpetually fresh regardless of how old the stain is.
To get to the stained wood, break into the storage facility after hours and break open the rooms one by one. Decae moves the square every few months to hide it from would-be plunderers. Eventually you will find the room with nothing but the square of wood inside. Take it outside of the building and set it on the ground. When the moonlight hits the stain, it will warp and twist until it forms the image of a flapper with a long and ragged gash on her neck that drools sticky-wet blood over her breasts. She’ll ask you to dance.
If you can dance with her until sunrise, keeping up with her dated but vigorous movements, she’ll vanish with the rays of the sun. Her movements will have cast her blood, red blood, all over your body and clothing. Although no one else will be able to see it, for the rest of your life you will appear bloodstained whenever you look at yourself. The applications of this should be obvious.