For   one, probably the uniqeness of what I'd call (and others may differ on) God's creations. I'd for example know every cat we had by their own ways even if they had looked identical. It may seem odd, us with cats and liking to see birds but (although I've never had one tame enough to come to my hand) I've sort of known friendly blackbirds and robins. Years ago on Conwy quay, I made friends with a seagull on the festival weekend. He would come to me, reject my offer of a chip but want a bit of my burger....

Most creatures I've known long enough seem to have their own distinct personality. Maybe it's "nothing" but when you sort of think in terms of just identifying, eg. this a cat, that is a crow, etc. but think they as well have their own "identities", maybe I get amazed.