Animals that are active primarily at night have eyes that are highly adapted with many more visual receptors than our human eyes. Each receptor requires lots of fresh oxygenated blood to keep it healthy and functioning.
All that fresh oxygenated blood is what makes eyes look red in a camera flash, and nocturnal animals win the prize for the reddest "Red Eye."
This Barred owl was at Springbrook's feeders looking for prey, using its very healthy eyes to search. I wonder if this is where the term "with blood in his eye" comes from?
This rabbit was eating at the same feeders a few days ago, but not at the same time. It's eyes are even bigger than the owl's eyes, and one of the blood veins within the eye can even be seen in this photo.
In the end, for nocturnal animals, the one with the best red eye wins all the marbles, and the loser is not in the gene pool any longer.