

I had the same thought.
Couple of possibilities:
Spoiler
-
Animals don’t seem to be infected in the same way humans are, and rats bite on their own anyway. Perhaps it was just a carrier rather than part of the hive. While it showed the same symptoms as later humans who became infected that doesn’t necessarily mean it was part of the hive. The zoo animals that were let loose definitely do not seem to be part of the hive (they attacked “them” who couldn’t defend themselves). We have no info if they went into the brief fugue state like the rat and the humans when they were initially infected.
-
If the rat was part of the hive, then it could just be the “biological imperative to spread” loophole that allows them to assimilate without consent.

























Two thoughts: