The eye position detector monitors light reflected from {HEAD ~ the users eye} to identify {TAIL ~ the pupil position} 
to identify
The eye position detector monitors light reflected from { HEAD ~ the users eye } to identify { TAIL ~ the pupil position }
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL