>I've seen my cat to be frightened by sudden appearance in the mirror just to relax in about 0.5 s. Clearly not enough time to decide if the creature in the mirror is harmless..

Why isn't it enough time to decide whether the reflection is harmless? Not my area of expertise, but I'd expect humans to be able to parse a face or a even posture for signs of imminent aggression in that time easily. Many other animals should be able to do the same.

I'd say we are highly optimized for this, since the biggest threat to humans have been other humans for most of history, and quick judgement can literally decide who lives and who dies.