In "Miss Brill," what explanations might there be for Miss Brill's thinking, in the last line of the story, that she "heard something crying"?

I must admit, I think the ending of this excellent short
story is rather unequivocal. Let us remember that we are presented with a woman who is
profoundly lacking in self-awareness, as her fantasy of the huge drama at the park
shows, in which even she is given a part and therefore importance. We are presented with
a female character who does everything she can to distract herself from her own
insignificance and lack of relations. She is overtly blind to this, but what is key
about the final paragraph of this tale is the way that at least part of her recognises
the truth of her own insignificance:

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But today she passed the bakey's by, climbed the
stairs, went into the little dark room--her room like a cupboard--and sat down on the
red eiderdown. She sat there for a long time. The box that the fur came out of was on
the bed. She unclasped the necklet quickly; quickly, without looking, laid it inside.
But when she put the lid on she thought she heard something
crying.

Key phrases to focus
on are the way which the room is described as being "like a cupboard," just as Miss
Brill, at the beginning of the story, looks at other people and imagines them to live in
rooms like cupboards as well. Also, note her response to her necklet that she took such
pride in at the beginning of the tale. She, at some level, is humiliated, embarrassed
and ashamed at what she overheard the young couple say about her as it resonates deeply
within her and makes her realise just how ridiculous and lonely she is. The crying at
the end of the story is therefore the sound of her own sobs.