{HEAD ~ Drum} 1 consists of {TAIL ~ a drum wall} 5 made thin and unstable 
consists of
{ HEAD ~ Drum } 1 consists of { TAIL ~ a drum wall } 5 made thin and unstable
HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH