{TAIL ~ The device} includes {HEAD ~ a continuous track} and a ball which is movable within and around the track 
{ TAIL ~ The device } includes { HEAD ~ a continuous track } and a ball which is movable within and around the track
TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH