Wilcox's clay bas-relief (symbol)
The clay bas-relief that Thurston finds in Angell's papers is the first intimation Thurston receives about Cthulhu's existence. The bas-relief, though it is a simple, modest object, strikes deep notes of fear and terror into Angell and Thurston's hearts, given how unusual the outline of the creature inscribed on it is. The bas-relief symbolizes not only the horrifying incomprehensibility of the Cthulhu cult writ large, but also the process by which the "Old Ones" transmit thoughts to sensitive dreamers to raise images in their minds. In this way, the bas-relief is also more specifically a symbol of the psychological "imprint" that the Old Ones have caused in Wilcox's subconscious.
Hoodoo (motif)
Lovecraft imagines Cthulhu and the mythology of the "Old Ones" as the driving cosmological force behind already-extant religious belief systems, such as hoodooo and conjure. As a well-known hub of voodoo belief systems and practices, New Orleans becomes one of the story's key settings, where Inspector Legrasse first learns of an otherworldly swamp in the hinterlands of Southern Louisiana. Lovecraft uses the supernatural and demonic reputation of voodoo as a way to suggest the power and mystery of Cthulhu.
Greek mythology (motif)
The city of R'lyeh is often described as having "Cyclopean" architecture, with gigantic and oddly shaped stones and buildings that do not conform to normal Euclidean geometry. The Cyclops were a race of one-eyed giants from Greek mythology who were descended from either Poseidon or the Titan Uranus (who predated the Greek gods). Polyphemus, the best-known example, is a character from the Odyssey. With one eye in the middle of his head, the exceedingly strong Cyclops resembled a human shepherd but actually preferred to eat human flesh. By suggesting that R'lyeh is something that a Cyclops might live in or inhabit, Lovecraft evokes not only the notion of something very large but also something extremely dangerous, lawless, and hostile, despite seeming potentially familiar.
Modern art (motif)
Lovecraft suggests that the cosmological forces of the Cthulhu mythos are part of the inspiration behind some of the prevailing schools of modern art in the early twentieth century—for instance, Surrealism, Decadence, Cubism, etc. In Lovecraft's universe, these aesthetically grotesque developments in contemporary art reflect psychological disturbances wrought by Cthulhu and the "Great Old Ones." Wilcox becomes a well-known decadent sculptor, whose forms aspire to render the "non-Euclidean" forms of the extraterrestrial beings in Lovecraft's tale.
White hair (symbol)
The only bit of information Thurston learns upon visiting Australia to investigate the saga of the Alert is that Gustaf Johansen's hair turned completely white upon arriving back at the mainland. White hair is classically a symbol of having endured some kind of psychological trauma, which Johansen did after being pursued by Cthulhu and narrowly avoiding death. Since Thurston has not yet read Johansen's diary when he learns this, the rumor suggests that Johansen sustained some kind of traumatic experience while at sea.
