Presenting a suggestion of heaviness to a person in a hypnotic trance (e.g., "your arm is getting heavier and heavier") tends to result in a corresponding change in the person's body position (e.g., the arm lowers). This phenomenon may be a result of activation of the mirror neuron system, which leads the subject to anticipate actual weight on the arm. The mirror system underlies people's ability to sense, in the absence of actual sensory input, experiences of other people. Perhaps this system allows the same anticipatory experience regarding non-human objects. In this study, we showed participants a picture of a rubber hand holding what appeared to be a lightweight rubber ball. In reality, the ball was weighted with sand. We instructed participants to move their arms to a horizontal position and hold them immobile. Those participants who knew the actual weight of the ball tended to raise their arms above the horizontal, perhaps in response to their expectation of the need to resist the weight of the ball. This illusional phenomenon might be similar to that induced by the hypnotic suggestion of heaviness. That is, the body's response may reflect activity in the mirror system, which anticipates greater weight
