moving {HEAD ~ the apparatus} and user along an indirect path away from {TAIL ~ a fixed starting point} 
moving { HEAD ~ the apparatus } and user along an indirect path away from { TAIL ~ a fixed starting point }
OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL