Bloody Mary has been thought to be the ghost of Queen Mary, or some other legend associated with the myth. According to legend, people can make Bloody Mary appear in a mirror if you: go into a bathroom and and turn off all the lights in front of the mirror. Say 'Bloody Mary' 3 times in a row. Turn lights back on, only to see Bloody Mary standing behind you. If you don't get out of the way, she will kill you and disappear.
The legend of Bloody Mary is often part of some american fraternity movie where a bunch of girls play tricks like pretending to be her, or as part of some initiation.
In Paranormal Activity 3, leading up to the scene with Randy and Katie, Kristi becomes feverish the morning after telling to stop talking to her because they played Bloody Mary the previous night. So, Dennis and Julie take her to the hospital and Randy is left to watch Katie. After the parents leave, he asks Katie what she would like to do. She suggests they play Bloody Mary. The two go up into the girls' bathroom, and shut off the lights. After chanting Bloody Mary three times, nothing happens, Randy turns the lights back on. Katie says they didn't wait in the dark long enough for anything to happen. So, they do it again. This time there is a noise, and when the lights come on, Randy has blood running down his stomach like he had been clawed in the chest. Becoming scared, Randy opens the door from the bathroom and an unseen presence knocks over the tea party table in the girls' room. After Randy quickly closes the door, Katie is crying and scared. Randy tries to comfort her, and opens the door again. This time, a silhouette speeds past the door.
