- Szpindel and Cunningham are both biologists, as is the author. Brüks in Echopraxia continues that theme.
The final lines were genuine symbolic-information-bearing content, but it only communicated for real when the lesser process managing its communications crypsis attempt noticed from the insult that it wasn't actually working. The completely neutral tone of most of the conversation made it seem like it was getting away with the deception (i.e. it was successfully engaging the Gang). Some kind of higher process then kicked in and it either changed strategy, or the more powerful engine finally recognised what was actually supposed to be going on and got it right. Either way, it can talk, but needs to be given a good reason to break its primary protocol before it will try. That's not what it was originally aiming to do.
- ...or it is simply another mode of the 'chinese room', one designed to instill fear and terror instead of merely distract and discourage. It might be merely a threat display, cribbed from thousands of hours of horror movie broadcasts.
Siri comes out of his hemispherectomy with deadened emotions, a Lack of Empathy, and a savant-like ability to pick up on subtle patterns in body language - All of these are traits associated with vampires, as are recurring epileptic seizures such as the ones that forced Siri to undergo surgery in the first place.
Siri is actually part-vampire himself, (likely on his mother's side, since she also demonstrates a few vampire-like traits.) much like the autistic children whose gene therapy gone wrong transformed them into the first reconstructed vampires. Prior to his hemispherectomy, the only notable effect his ancestry had on him was making him vulnerable to the cruciform glitch, though to a lesser extent than full vampires, which was the true cause of his seizures. After his surgery forced his brain to radically rewire itself, Siri was cured of the cruciform glitch but overall ended up a lot more neurologically vampire-like than he was before, causing his extreme shift in personality.
In keeping with the Central Theme of the book, Siri's unconscious mind has figured this all out, but his conscious mind hasn't yet. His extreme paranoia regarding Sarasti and vampires in general is a result of him subconsciously projecting his own self-loathing about being a "zombie" onto beings who remind him of himself.
