Despite being explicitly instructed to resist, a patient's arm can be moved into any position with no resistance at all, and immediately returns to its original resting position as soon as the examiner lets go. What is this?

This is Mitmachen (cooperation): the body can be passively moved into any position with no resistance despite an explicit instruction to resist, and, crucially, the moved part returns to its resting position once released rather than staying where it was placed. It is not waxy flexibility, in which a posture is actively maintained once placed there rather than springing back. It is not Gegenhalten, the direct opposite pattern, in which the patient resists passive movement with matching force. And it is not automatic obedience, which concerns compliance with verbal instructions rather than passive limb positioning.