Check out the dog, Barley, in this video. Notice how he doesn't seem interested in the food on the left side of his bowl. Perhaps he's blind in his left eye?
But that can't be the case. Close your left eye. You can still see much of your left visual field, and you'd certainly smell any food placed under your nose. And what dog is one to walk away without finishing their food?
In fact, Barley is displaying signs of hemispatial neglect, a strange condition in which brain damage, despite normal vision, results in complete neglect of the left side of one's world. Barley had, in fact, suffered a stroke.