Certain masses oscillating about the z axis are tiltable about the x axis, while {HEAD ~ some others} are tiltable about {TAIL ~ the y axis} 
are tiltable about
Certain masses oscillating about the z axis are tiltable about the x axis , while { HEAD ~ some others } are tiltable about { TAIL ~ the y axis }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL