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