{HEAD ~ The contraction} of spring 20 causes {TAIL ~ needle} 14 to be retracted into the void space 15 in sensor base unit 18 
causes
{ HEAD ~ The contraction } of spring 20 causes { TAIL ~ needle } 14 to be retracted into the void space 15 in sensor base unit 18
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH