In this way, {TAIL ~ material} impaled upon {HEAD ~ a bar} is slid or scraped upwardly towards the top of the bar 
In this way , { TAIL ~ material } impaled upon { HEAD ~ a bar } is slid or scraped upwardly towards the top of the bar
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH