In other words, except for chimpanzees, cryonics patients, Terry Schiavo, and babies who are exactly 1 year and 2 months and 5 days old, there isn't much that's ambiguous between person and non-person.

Slightly offtopic, but doesn't that assume personhood is binary? I've always assumed it was a sliding scale (I care far less about a dog compared to a human, but I care even less about a fly getting it's wings pulled off. And even then, I care more than about a miniature clockwork fly.)