"Arm drop", or the "face-hand test", has been suggested as a useful diagnostic test if hemiparesis or upper limb monoparesis is suspected to be psychogenic: the examiner lifts the paretic hand directly over the patient’s face and drops it. It is said that in organic weakness the hand will hit the face, whereas patients with functional weakness avoid this consequence. However, the validity and reliability of this "avoidance testing maneuver" has never been examined; its clinical value is therefore doubtful.
Stone J, Zeman A, Sharpe M. Functional weakness and sensory disturbance. Journal of Neurology, Neurosurgery and Psychiatry 2002; 73: 241-245