Regarding Adventure Time, there is a character called Jake the dog. It's always bugged me not knowing why his eyes are white where the pupil should be, and black where the iris should be (i.e. inverted).
I used to think he was wearing some really thick monocles in both eyes, but they do seem to "twinkle" every now and then (but given how weird adventure time is, I wouldn't be surprised if these monocles could twinkle like normal eyes - assuming they are monocles):
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I know, I thought so too when I first saw Jake. But it turns out his eyes are not inverted. The sclera of his eye (aka "the white of the eye") isn't shown. The whole eye is drawn black, as can be seen on dogs whose eyes are not turned at extreme angle and the white circle we see is reflected light, like on this random stock photo of a dog (not the same model as Jake):
This light reflected in the eye is apparently also called "Catch light", so Jake's eyes are ~80% that.
