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Multiple sources on the internet (including answers on this site) claim that red-eye is created by light from the flash reflecting on the blood vessels in back of the eye.

So, why do animals like dogs, that I believe also have red blood (I'm not going to injure my dog in order to test this, but I'm pretty sure the blood is red) have green-eye?

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    \$\begingroup\$ Maybe some sort of vegetation growing on the back of pet's eyes reflecting the light? \$\endgroup\$
    – Nir
    May 2, 2011 at 13:35
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    \$\begingroup\$ ...and lets not forget Riddick \$\endgroup\$
    – Jakub Sisak GeoGraphics
    May 2, 2011 at 15:24
  • \$\begingroup\$ +1 for not injuring your dog. (Also, good question :P) \$\endgroup\$
    – poke
    May 2, 2011 at 17:59

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Many animals, including cats and dogs, have a reflective layer of cells at the back of the eye called the tapetum lucidum ('the tapestry of clarity'). This reflects the light back through the light-sensitive cells in the retina for a 'second pass', allowing the animal to see better at night.

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  • \$\begingroup\$ You don't have to do photography to notice this green reflective layer; staring into a cat's eye at exactly the right angle will let you see that at naked eye :) \$\endgroup\$
    – badp
    May 2, 2011 at 18:17
  • \$\begingroup\$ Yup, headlights are particularly effective at showing them up. \$\endgroup\$
    – ElendilTheTall
    May 2, 2011 at 18:49
  • \$\begingroup\$ Nice answer, +1, but no one as yet has explained why the color is green specifically... \$\endgroup\$
    – Uticensis
    May 2, 2011 at 20:47
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    \$\begingroup\$ @billare: actually, eyeshine can be white, green, blue, yellow or pink, depending on the angle you view it at. \$\endgroup\$
    – ElendilTheTall
    May 2, 2011 at 20:57
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According to Wikipedia it seems that animals that exhibit this phenomenon ("eyeshine") have an extra layer of tissue within their eyes that cause light to be reflected in a different way.

enter image description here
Source: Wikipedia

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    \$\begingroup\$ Wikipedia has a picture of a cat which dramatically illustrates red eye and "eyeshine" occurring simultaneously. \$\endgroup\$
    – mattdm
    May 2, 2011 at 14:03

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