I’m pretty sure most adult dogs and cats understand mirrors, they just get creeped out by their own reflection. Take an adult cat, hold it up to a mirror. Watch as it actively avoids looking at itself. My dog stares at me for long periods through a full-length bedroom mirror and even barks and runs to the window when she sees dogs outside through it. Doesn’t really care much about her own reflection.
My idea is to train several A.I.s on mostly religious ideology, a single religion for each. Then let them converse with each other.