{HEAD ~ Two electrical cables} of an articulated robot arm are in {TAIL ~ the form} of helical cords which lengthen and shorten respectively during the rotation of the arm 
are in
{ HEAD ~ Two electrical cables } of an articulated robot arm are in { TAIL ~ the form } of helical cords which lengthen and shorten respectively during the rotation of the arm
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH