Ulysses: Metaphor Analysis

Keys
Keys are alluded to several times in the novel when, for instance, both Bloom and Stephen spend the day without theirs and Bloom attempts to secure work with the firm called Keyes. The key come to symbolize security and closure, and the lack of these objects reinforces how both Bloom and Stephen are exiles, figuratively homeless, in their own land. Furthermore, by not bringing his key when he leaves the house, Bloom highlights his outsider status all the more: his isolation is increased.
However, there is also a sense of liberation invested in these two characters as they wander the streets of Dublin free of the symbolic representation of home. Without their keys they are represented as wanderers rather than fixed in their role in society.
Prostitution
The notion of women selling their bodies for sex is referenced through the course of the day and is most notable in the episode entitled 'Circe'. As well as these literal inclusions of prostitutes in the texts, passing comments are made which draw a symbolic parallel between prostitution and Ireland selling her land (body) to the highest bidder.
Throwaway
This is the name of the horse that won the Ascot Gold Cup and is inadvertently the named cause of disagreement in the 'Cyclops' episode when the men in Barney Kiernan's pub turn against Bloom. They mistakenly believe he has won on it and is holding back with his generosity in buying the drinks. The men are quick to believe this of Bloom, which demonstrates how their anti-semitic prejudices need little excuse to surface.
Throwaway is also a symbolic name for the outsider as it refers to garbage. Throwaway is also the 'dark horse' that wins the prestigious race at odds of twenty to one. Both of these readings may also be aligned with Bloom, who is treated as an outsider by many of the characters, but is also favored in the text for his curiosity, rationality and refusal to be bigoted.