Pic! (The Real Unicorn by wangkingfun, from 2015)

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Actually image found not by me, just was posted in this thread

I fairly lightly wondering if this 'invisibility' by 'normal' humans in original (as popularized lately) legend was partially protection spell, but partially hint to readers about their unability to see wonderful in that they assume was casual, and about to be exploited (horses/mares being of course slaves for human civilization, rhetorics not standing up to reality)