Thus, the number of times {TAIL ~ gas} escapes from {HEAD ~ the valve} can be counted 
Thus , the number of times { TAIL ~ gas } escapes from { HEAD ~ the valve } can be counted
OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH