Walking with eyes closed and ashplant hanging "by my side," Stephen thinks, "Tap with it: they do." Who is "they"? The book will retrospectively confirm a common-sense answer to the question: blind people tap the ground with sticks to see where they are going.
In Lestrygonians Bloom crosses paths with a "blind stripling" who stands "tapping the curbstone with his slender cane." (The stripling will reappear in Sirens, where the "tap" sound of his wand becomes a musical motif in the chapter's play of sounds.) After he has helped the unfortunate young man cross the street, Bloom tries to imagine how blind people sense presences in space, how they manage to walk a straight line, how they compensate for their disability, and how their other senses may be augmented. Soon he is touching various parts of his body to see what touch can do independent of sight, and thinking, "Want to try in the dark to see." Stephen's tapping with his eyes closed seems to connect with Bloom's efforts to imagine what it is like to be blind—one of many esoteric correspondences between the two men in the novel.
§ Declan Kiberd reads another kind of significance into "Tap with it: they do." The ancient Irish bards, he notes, also tapped with sticks: "Once upon a time in ancient Ireland the bard was a powerful figure, standing second only to the chieftain. But those days are long gone, and Stephen is utterly marginal in the colonial society which has since emerged. Yet he carries an ashplant walking cane to evoke memories of those filí who carried a rod as a symbol of their vatic power. Those filí were often blind or short-sighted, so the rod helped them to feel their way forward, as the stick assists Stephen" (Ulysses and Us, 32).
Kiberd observes that Mulligan has called Stephen a bard several times in the book's first chapter, and Stephen recalls these mocking invocations at the end of "Nestor": "Mulligan will dub me a new name: the bullockbefriending bard." He also supports his contention that Stephen is thinking of the ancient bards by observing that when Joyce carried his cane through the streets of Paris, matching the dress of fashionably decadent flâneurs, he insisted on the Irishness of his ashplant: "'It was a symbol of his country,' said Jacques Mercanton, 'that he always carried with him on the roads of the world'" (32-33).
To this argument one might object that Stephen thinks, "Tap with it. They do," not "They did." But the ancient Irish bards' powers of prophecy would cohere with the Roman powers of divination that he summons later in Proteus when he thinks of an alter-self sitting on another planet "with his augur's rod of ash."