As it was explained to me by Dr. Kawasaki, a green stool means the food
moved quickly through the digestive system.  It can be indicative of any
number of problems or just a non-problematic occurance.  If all you get
is the one loose green stool I wouldn't worry. If it persists for a while
you should be concerned.  After you've had ferrets for a while you can
sort of tell when you need to be concerned pretty easily.  You also look
for other signs of illness like lethergy and changes in eating habits.  A
change in foods is one of the causes of some looseness and greenness in
the stool also.
 
I imagine the good doctors around here might have something more to say
though.
 
bill and diane killian
zen and the art of ferrets.
[Posted in FML issue 1210]