Neck fat neck
As William Brayden ascends the stairs, Bloom sees "Welts of flesh behind on him. Fat folds of neck, fat, neck, fat, neck." The second sentence, Seidman notes, is an example of epimone: "persistent use of the same word or words."
Coming from Greek epi = "upon" + meno = "to remain" or "dwell," hence "a staying on" on "dwelling on," epimone also has the Latin name perseverantia. Shakespeare is famous for examples like Iago's "put but money in thy purse" and Antony's "For Brutus is an honourable man." As a rhetorical tool, the point is usually to persuade or excite passion by repetition and variation. Joyce's mind-numbing phrase performs no such effect.