Sticking point, in an idiom WSJ Crossword Clue

Think of what might irritate a bird if it can't quite digest it.

???? is the crop or throat of a bird, where food is temporarily stored.

The clue refers to the idiom 'stick in one's ????,' which means something that is hard to accept or causes persistent irritation. '????' is a part of a bird's throat where food is stored, and the expression metaphorically describes something that is difficult to swallow or get over.

Stick in one's ___ (bird-related idiom), Where something irksome might stick, Idiomatic sticking point, insect's stomach, Where something rankling might stick