When Bloom steps into the outhouse, "bowing his head under the low lintel," his action is possibly meant to echo a line in a poem published in 1904 by Henry Van Dyke, praising the low lintel of a friend's house as a sign of humility. Unlikely as the allusion may seem, it is amplified by the description several sentences later of Bloom "Asquat on the cuckstool."
Van Dyke, born in 1852, was a prominent American clergyman and professor of literature. His high-minded poetry, given to stale abstractions and unrelentingly uplifting sentiments, seems an odd candidate for anything but ironic inclusion in Ulysses, but Inscriptions for a Friend's House does bear an obvious similarity to the sentence in Calypso. The first two of the poem's four sections go as follows:
The cornerstone in Truth is laid,
The guardian walls of Honour made,
The roof of Faith is built above,
The fire upon the hearth is Love:
Though rains descend and loud winds call,
This happy house shall never fall.
The lintel low enough to keep out pomp and pride:
The threshold high enough to turn deceit aside:
The doorband strong enough from robbers to defend:
This door will open at a touch to welcome every friend.
Thornton acknowledges that "the allusion seems perhaps unlikely," but he argues that "'He went in, bowing his head under the low lintel' in depicting Bloom's defecation (which he spares Stephen), contributes importantly to our impression of Bloom as a man without 'pomp and pride.'"
By describing the privy seat as a "cuckstool," Joyce amplifies the sense of abasement. The cucking-stool or cuckstool was a late medieval and early modern form of punishment. Overly talkative women and dishonest tradesmen were tied to a chair and set in front of their houses to be jeered by passersby, or ducked in a pond or river. The OED notes that sometimes the chair took "the form of a close-stool," i.e. a chamberpot enclosed in a wooden chair or box. By showing Bloom on the privy, the novel subjects him to just this kind of humiliation.