Scary Optical Illusion

The gimmick of making two people look like a skull has been around for more than a century. Maybe even longer, but I haven't seen any proof of it. The image shown here, A Pierrot's Love, is one of the oldest examples (1905). It's also on the ambiguous skulls page. Pay special attention to the detail of the image : the glasses that become teeth, the sleeves become a nose ... it all works out. Which makes it the mother of all scary optical illusions to me.