Standing in a darkened room lit only by the light of a candle, her name must be chanted three times in front of a mirror. Bloody Mary, Bloody Mary, Bloody Mary.

Peering into the darkness in the mirror, a figure will then become apparent as the spirit of the sinister Bloody Mary has been summoned.

So goes the infamous ritual that is well-known throughout the world and which has terrified teenagers slumber party guests for decades. For some, it's a fun joke, an opportunity for pranks, for others it's a sinister superstition, a legend that should not be taken lightly.

The details of the ritual differ depending on the telling of the tale, and the exact identity of the creature summoned changes—ghost, witch, re-animated corpse.

In some stories, the creature crawls out of the mirror and claws out the eyes of the person who summoned her, in others she remains a terrifying but harmless reflection.

The one thing that remains among all common retellings of the story is that the ritual is a dangerous activity to take part in, and Bloody Mary is not a creature that you want to find yourself face to face with.