In addition to the number and ratio of rods and cones in an animal's
eyes, there is another mechanism that enhances night vision.
 
There is a membrane(I can't remember its name) that in essence bounces
light back inside the eye for a second pass. This membrane is not
present in humans which have poor night vision but present in other
animals which see very well in low light conditions.
 
Any animal with this mechanism displays "eye shine" back to a light
that's pointed at them such as car headlights at night.
 
Ferrets display eye shine because they have this mechanism. So whatever
quality of vision they have, is not diminished by low light as
drastically as we humans.
[Posted in FML issue 1281]