These units may also have {HEAD ~ other pieces} such as microphones and {TAIL ~ speakers} in order to allow communication to be facilitated in difficult circumstances 
such as
These units may also have { HEAD ~ other pieces } such as microphones and { TAIL ~ speakers } in order to allow communication to be facilitated in difficult circumstances
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH