Though the sea is only mentioned once in this poem (in line 18), it is constantly on our mind. It is hard for us to separate anything having to do with The Odyssey from the sea, because so much of Odysseus' journey goes down on the ocean. We also can't help but feel just a little sorry for Circe, who we know lives all alone on an island in the middle of the ocean. That's got to be rough and not a little bit lonely. The sea's presence in the poem makes us both anxious and lonely. We imagine Circe looking out at the sea, watching Odysseus sail away.
Line 18: Here, the sea is personified as Circe describes it as "crying" and "pounding." We know that she means to describe stormy conditions, but her word choice here (in a time of Olympian gods) makes us think twice.
While pigs are the only animals that feature in this poem, we do know that in The Odyssey, lions and wolves also roamed around Circe's house. Animals feature largely, for Circe's famous for her ability to transform men into animals with a flick of her magic wand. In this poem, she draws a distinct connection between animals and humans, arguing that there are times when humans behave like animals (and in those cases, she just helps them by making them look like the animals they mimic).
Line 2: A "pig" is a metaphor for an uncouth person (the opposite of James Bond). When Circe says, "Some people are pigs," we see a paradox.
With all of this talk about what is real and what is an illusion, magic features largely. Circe argues that she uses her magic to expose the truth (i.e. make men who act like pigs literally look like pigs). Circe's power (title alert!) is her ability to practice magic, but there are times in this poem when her magic doesn't seem to work, and when she relies instead on words.
Line 23: "Hold" is a pun. In this moment, "hold" means both to literally hold someone in your arms and to figuratively keep them prisoner.