I was sitting in the upstairs office of the museum with a cup of coffee when it happened. It had been a long day and I'd set the work experience kid the seemingly unfuck-up-able task of dusting the exhibits - after repeating my warning, of course, that some of them must not be touched or opened. A terrified scream, quickly strangled by a building-shaking thump and an awful rending sound, brought me rushing downstairs.
The mirror room - I knew it. In there hung an ancient mirror, about a foot around, made of polished obsidian. Behind the glass walls of its display case, it was harmless, although people amusingly reported seeing the face of an evil hag in it on occasion. Looking at it unprotected was madness, though - certainly for those without knowledge of the old ways.
I arrived in the mirror room and a horrible smell hung in the air. On the floor lay half a body - the lower half, still in the clothes I recognized from earlier. The skin had been stretched purple and torn away and the organs inside that hadn't been torn free leaked their contents onto the floor. The legs were at the bottom of a maroon spray that started below the wooden case of the mirror, and the hipbone lay almost against the wall.
The case was broken, the wooden sides pushed outwards. Clumps of hair, matted with skin and blood, stuck to the frame of the mirror. Concentrating now, I stepped in front of the black disc, my sandals carefully placed on either side of the bile-sprayed limbs and pool of blood on the floor. Looking into the dark reflection of the room, I saw my double once more. In her hand was a pale arm that led down to a broken form and a trail of darkness. Sure enough, when she lifted the half-corpse into the air, I recognized the shattered and stretched face.