The ouija board has been explained by 'skeptics' as an ideomotor effect.
http://www.skepdic.com/ideomotor.html
Strangely enough, I just don't buy it (the ideomotor explanation that is).
I think it is reasonable when explaining dowsing. A tiny unconscious movement can cause a big movement in the tensed twig or the precariously balanced coathangers.
However, the force required (to move a glass and 3 other arms) and the spelling of words seem to be well beyond anything that be done subconsciously.
So my assertion is that when the pointer moves, at least one person is deliberately moving it to spell out a word.
Clearly, even those who are attached to ideomotor explanation must admit that in the course of the history of ouija sessions, some have been moved by the deliberate action of an attendee.
Is there any experiment or test that could be performed that is capable of convincing an independent 3rd party (me) that what we're seeing is ideomotor and not someone having some fun?