According to Lilienfeld et al (2012)
“… FC is a striking case of the ideomotor effect, which had been known in psychological circles since at least the mid-nineteenth century. This effect, illustrated by such purported paranormal phenomena as Ouija boards, automatic writing, table tipping, dowsing, and the Chevreul Pendulum, refers to the propensity of people’s thoughts to influence their movements without their awareness. By means of mutual operant shaping, the facilitator and subject gradually learn to adjust to each other’s subtle movements. Over time, facilitators become convinced, and frequently insist, that they are merely offering resistance to the child’s hands, not actively guiding them. Yet, the data on FC clearly demonstrate that they are in control, even though they are typically unaware of their inadvertent authorship of the messages. This problem of unconscious bias and signaling has sometimes proven difficult to manage even for researchers trying actively to minimize it".