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