"Pestilential tempests" (simile)
When Legrasse and his men approach the Cthulhu worshippers, they hear chanting noises that Legrasse compares to "pestilential tempests." The simile comparing ritual chanting to the buzzing of insects is an allusion to the plague of locusts that descend upon Egypt in the Book of Exodus. The simile suggests that the ritual chanting augurs the annihilating power of a supernatural force, not unlike the various plagues that God causes in the Bible.
Barn door (simile)
Johansen describes the entrance to Cthulhu's monolith as being like a great barn door, given its, "ornate lintel, threshold, and jambs." The simile of the barn door suggests, first, the enormity of the door, and second, the fact that it conceals some kind of animal or creature inside.
Smoke (simile)
When Johansen and his men manage to figure out how to open the door to Cthulhu's resting place, Lovecraft writes that darkness billows forth like "smoke" from inside its chamber. The simile suggests darkness made material, a phenomenon that Johansen struggles to describe in his diary, and which symbolizes the larger idea that the cosmological forces at hand cannot be apprehended by human eyes and ears.
Cyclops (allegory)
After Cthulhu emerges from its resting place, Lovecraft describes its demeanor as "bolder than the storied Cyclops." The allusion to Greek mythology suggests that Cthulhu is at once ancient, massive, and of unfathomable power. Because Cthulhu comes from the outer reaches of the galaxy, its mightiness surpasses even that of the mythical creatures imagined by the Greeks.
Mountain (metaphor)
Near the end of the tale, Lovecraft writes, "A mountain walked or stumbled," to describe Cthulhu's awakening. The metaphor of a mountain moving like a human suggests the vast scale of Cthulhu's otherworldly body, and also the lack of detail with which Johansen is able to describe its form in his diary, likening the monster to a massive geological structure.
