What the speaker “heard” in this line is the pallbearers (people who help carry the casket at a funeral) lifting the “Box,” or coffin. The coffin can symbolize different things depending on interpretation. If we read this poem as being about the speaker’s descent into madness, the coffin may be carrying the speaker’s formerly “sane” self. If the poem is the speaker’s imagining her own death and funeral, the coffin contains her corpse as she imagines it.
