The ideomotor effect is a psychological phenomenon where a person makes movements unconsciously, often in response to their thoughts or expectations. This effect can lead to subtle muscle movements that the individual is not aware of, which can influence actions like the movement of a pendulum or a pointer on a device, such as a Ouija board. This effect is commonly observed in various activities, including hypnosis and kinesiology. It highlights how the mind can influence the body without conscious intent, demonstrating the connection between mental processes and physical actions.