pa/ca correspondence (Kirikae 1994): central/western Hokkaido par/paro :: eastern Hokkaido + Kuril car/caro 'mouth' (also icaroyki :: iparoyki 'feed', aycaro 'arrow nock'). Shiratori (2026) derives this pa- :: ca- alternation from a Proto-Ainu diphthong *pia 'mouth' — the same *pia that replaces ALTT's palatalized *pʸ. Well grounded as a correspondence; the *pia reconstruction is Shiratori's proposal.