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However, I agree that Agilus, when slaughtered, appears to be flesh and blood---a lot of blood. Even if chems have blood, it would smell and flow differently. Severian would notice.
Perhaps Agilus and Agia are false names and they are not twins at all, one a chem and one a human. This is not as neat as if they were indeed twins, but it's plausible---they are deceptive people.
If I remember correctly, chem blood is described in the Long Sun books as 'black fluid' and 'oil' which would rule out Agilus as an android/chem.
I do agree that chems in the Long Sun are the same sort of technology as Jonas.