Poe opens "Berenice" with an epigraph that foreshadows the eventual end of the tale:
Dicebant mihi sodales, si sepulchrum amicae visitarem, curas meas aliquantulum fore levatas. —Ebn Zaiat
This Latin epigraph translates to: "My companions told me that if I visited the tomb of my beloved, my grief would be in some measure relieved." The inclusion of this epigraph explicitly predicts the horrific events that will come to pass at the end of the story. The passage marks Poe’s first reference to death and misery—subjects that haunt and permeate the narrative.
Three key moments of “Berenice” are foreshadowed in this epigraph: the visitation of a grave, the death of a loved one, and the relieving of the speaker’s grief “in some measure.” Egaeus’s “visit” to Berenice’s grave at the end of the story fulfills all three components of the epigraph’s prediction. First, he literally goes to the spot where Berenice is buried, even if subconsciously and under the influence of his madness. Second, in doing so, Egaeus is finally able to possess the objects of his desire and all-consuming focus (Berenice’s teeth) and, thus, is able to relieve his grief at her supposed death. Furthermore, by disturbing her grave, Egaeus unwittingly makes it possible for the servants to discover that Berenice is in fact alive, therefore removing the need for grief altogether but leaving horror in its wake.
What's more, the epigraph hints that Egaeus sees Berenice as his “beloved.” This fact is especially interesting in light of the following passage:
During the brightest days of her unparalleled beauty, most surely I had never loved her. In the strange anomaly of my existence, feelings, with me, had never been of the heart, and my passions always were of the mind.
Although Egaeus claims that he had “most surely […] never loved” Berenice, his own actions toward her hint at the opposite. His memories of her as a young woman—“agile, graceful, and overflowing with energy”—suggest a degree of fondness even he might be unaware of (or unwilling to admit), and his later interest in her physical state over the course of her illness may be read as the manifestation of his repressed desire for her. Thus, the epigraph introduces the possibility of Egaeus’s love for Berenice before he himself can attempt to deny it.
Finally, the epigraph reappears near the end of the story, just before it is proven true. Right before the menial arrives to inform Egaeus about the tragic, horrific fact of Berenice’s survival and defacement, Egaeus reads the words in an open book laid out on the table next to him. The line is even underlined (it is implied that Egaeus did this himself), thereby reinforcing the words and the connection they have to the situation in which Egaeus now finds himself.
In the following passage, Egaeus details some symptoms of his monomania, including his tendency to lose track of time:
to lose myself, for an entire night…; to dream away whole days…; to repeat, monotonously, some common word, until the sound, by dint of frequent repetition, ceased to convey any idea whatever to the mind; to lose all sense of motion or physical existence.
Although Egaeus describes these signs as some of the “least pernicious” changes brought on by his disease, in fact, this moment directly foreshadows the exact circumstances that lead to his violation of Berenice. Here, he establishes his habit of losing himself for hours and even days on end in the ceaseless study of mundane objects, which hints at his future obsession with Berenice’s teeth. His impulse to repeat words until they lose any semblance of meaning predicts his later declaration: “que toutes ses dents étaient des idées,” which in English means “that all her teeth were ideas.” In this way, he turns her teeth, like ideas, over and over in his mind until they are not teeth at all but “substances” he must possess at any cost.
Even more terrifying than Egaeus’s lack of control over his obsessions is his spotty memory, which results in the inability to trust his own mind. He's aware that through his “distempered vision” the objects that catch his undivided attention are “invariably frivolous,” but he continues to place extreme and disproportionate importance upon them. Egaeus is caught in a double bind: trapped by the knowledge that his own mind is suspect yet unable to determine the extent of his delusions, he is doomed to watch as his illness outstrips his will.