I would say that the song Bromden sings that gives the title to the book might be one significant metaphorical interpretation. The singsong chant of Bromden's grandmother gives insight to the novel's title and its themes:
one flew east, one flew west, one flew over the cuckoo's nest . . . O-U-T spells out . . . goose swoops down and plucks you out.
The idea of resistance is a dominant idea in the novel. McMurphy, and then Bromden himself, both seek to represent resistance against the authority structure of Nurse Ratched. The idea of fighting through the "goose" who "swoops down" is something that both characters seem to embody. In a larger sense, Bromden's grandmother's chant is something that applies to all individuals who do struggle. Consciousness and being in the world is a form of resistance, fighting against authority structures that seek to control and dominate, battling against the "goose" that has a tendency to "swoop down" against all human beings. In this light, Bromden's metaphor carries a large significance.