The surprise popularity of summer's horror hit Ouija shows that the favorite 19th Century occult pastime still holds sway in 2015.
Still... does a ouija board actually work? The prime scientific explanation for the ouija phenomenon is the ideomotor effect. As Skepdic explains:
Muscular movement can be initiated by the mind independently of volition or emotions. We may not be aware of it, but suggestions can be made to the mind by others or by observations. Those suggestions can influence the mind and affect motor behavior.
Basically, human beings are very suggestible. The nervousness engendered during a ouija situation creates a very small unconscious movement in the muscles, which, when many people move the pointer without knowing it, makes an eerie, gliding movement in the ouija board's pointer.
The discovery of the ideomotor effect is credited to William Benjamin Carpenter, who wrote a paper on it in 1852. It is sometimes referred to as the Carpenter effect for this reason.