Swheat Scoop litter clumps because of the wheat proteins in its name.
There are no chemicals, or other ingredients for that matter.  (If you
look on the side of the bag, the 'ingredients list' consists of one
word, wheat.)
 
If your ferret tastes Swheat Scoop to determine its food value, that's
fine.  As long as your ferret isn't eating any great quantity of Swheat
Scoop, it is perfectly safe.  If your ferret IS eating quantities of
any litter, it isn't going to be safe.  That includes cellulose-based
litters, such as those made from newspaper.
 
If your ferret does tend to eat his litter, he most likely has a
deficiency and needs to see his vet immediately.  The situation is
no different from a dog that eats feces and grass.  A ferret with a
balanced diet won't feel the need to eat his litter.
 
Gale
 
"Don't smile at me like that! That's not even a real smile; It's just a
 bunch of teeth playing with my mind!" Lt. Templeton Peck
[Posted in FML issue 4521]