Janet Leigh's Shower Curtain

Origins
A classic, white shower curtain, there is some speculation whether this was the one used in Mr. Hitchcocks' home or the one used in his famous film, Psycho.

Effects
Whenever the curtain is hung out so at least part of it is a screen, a shadowed figure materializes on it even if there was nothing behind it before. Touching the curtain or even being near it when the shadow is there results in stab wounds to appear on the closest part of the body to the curtain, the cuts being deeper the closer to the curtain. These can be fatal. The only way to deactivate the artifact is, coincidentally, to throw chocolate onto the curtain.