The thin end of the shell of an oyster. For an oyster opener, there are five terms to know about an oyster: Beak, hinge, bill, adductor, cupped. The beak is the pointed part of any oyster. Right behind it, the hinge is found. The adductor is a powerful muscle that holds the oyster shut. The bill is the broad flat end opposite the beak. The cupped portion is the "more bellied" shell half of the two oyster shell halves (called valves). That cupped shell is always facing down when opening any oyster.