The parasite-of-unknown-origin soon begins communicating with our hero, spouting eyes and mouths on his fingertips or palms to suit his purpose (and presumably small vocal chords inside to allow it to speak). The creature, which takes the name Migi (for "right"), is a calculatedly comical looking creation, and it's clear that at one level he's meant to stand in for the awkwardness of young adolescent body change. In one early sequence, for instance, the curious parasite hand tries to give Shinichi an erection as he stands before a public urinal to see what the experience is like. Our good-hearted hero is not at all amused.
Writer/artist Iwaaki plays his hero's adolescent travails for knowing chuckles, and there are plenty of moments that read more like high school comedy than they do terror. Which is not to say that Parasyte stints on the shape-shifting horrors: to remind us of the ever-present peril, we regularly cut to other host bodies as they attack and feed on their human victims. To Shinichi, this act smacks of cannibalism, though the non-human Migi doesn't see it that way. To its "mind," singly focusing on devouring on humans is natural and amoral. Unlike humans, who seem to be willing to "eat anything," his appetite appears to have a specific natural function: to regulate and thin out the human population before it completely trashes the planet.
Iwaaki's art is generally more expressive when it comes to rendering his title creatures than it is his human figures – who frequently are given the same facial expression in more than one panel on a page. But in a way this stunted affect works to maintain the flat drive-in movie vibe of his story. (It also helps to reinforce the pod people element of the story since the art provides no real clue as to who is human or host body until they reveal themselves.) While there are other manga artists out there capable of producing more evocative, lingering horror comics (cf., Hideshi Hino, Junji Ito), there is a sort of Sci-Fi Channel appeal to the way that Iwaaki depicts both his gory horrors and his scenes of teenaged angst. By the time the first book introduced a shapely female host masquerading as one of Shinichi's teachers, I was ready to follow this B-movie manga to its conclusion. Wonder if John Carpenter'd consider doing the movie version?