Episode 3A “Nanozim” is about bodily anxiety. It makes sense; children around Dib and Zim’s age (or what Zim’s intended age is supposed to be at any rate) are naturally anxious about their bodies and the imminent changes which puberty will force.
But this is a bit too dry of an analysis for an episode which features Zim shrinking and inserting himself into Dib’s body so as to erase information on the location of a data file which incriminates him. Even more so when later episodes are watched and you, the watcher, glean that episodes featuring bodily concerns are quite prominent in the series. So, in order to understand what each episode featuring bodily preoccupations is actually about, we need to focus in on some details.
I would posit that “Nanozim” is overdetermined by friendship, specifically, the sort which hides itself through desperation and the idea of a ‘frienemy” (someone who is a friend but also an enemy). All though Zim, as displayed in 2A “Bestest Friends” appears to desire little need of friendship, this is likely because the person he wants to be friends with is not Keith, but rather Dib, that narcissistic other who would make a perfect companion to his existence.
Needless to say, this is why the sequence is overflowing with coercion and violation; why Zim hides himself in Dib’s food, why he hijacks Dib’s arm and erases the information from his mind; it is why Dib, responding to Zim’s intrusion, retaliates with his own nanobot so as to engage in that time honored homoerotic tradition—physical one-on-one combat. Suitably, this is also why Zim is expelled from Dib’s body by Dib either urinating or defecating, both of which hint at the pre-sexual fascination with the phallic.
Of course, it is a show featuring children. So no sexual desire is present insomuch as the signs indexing the sexual connotations of the Zim-Dib battle hint at a possible erotic future. As they stand, however, what these signs hint at is a fascination with invading personal spaces; territorial incursions which derive from a longing for companionship.
What is significant? Each protagonist is male. Female presence is banished (Zim is alone in Dib’s body, whereas Gaz is pushed aside and only takes command once Dib becomes incapacitated). But, a distanceis maintained; in true homoerotic longing, a space is created between each of the desiring subjects, a space which allows for the two combatants to duke it out, yet still preserve their sexual autonomy (the indication on whether they are sexual subjects acting on impulses, that is). This is done via recourse to the nanobots—they allow the boys to fight each other, and be extremely close to one another, closer even than many sexual partners, yet still maintain a distance precisely to their extreme closeness. An interesting form of smothering.
Zim controls Dib’s arm. Would it not be possible for Zim to control other parts of Dib’s body? Meaning, why would Zim just not force Dib to commit suicide? Why merely erase knowledge of the file instead of physically removing his opponent? Furthermore, why would Zim announce his presence at all? If he was truly deadest on erasing the information from Dib’s brain, why not mosey on around insider his body without alerting his foe? I think the answer is obvious—Zim wants the confrontation between Dib. Though it may not be the ideal romance (or romance at all!), or even a practical way to appreciate your actual bestest friend in the whole universe, it is better than not announcing your feelings at all.