Do Dogs Get Sick Eating Walnuts?

Yes! Walnuts are poisonous to dogs.

Walnuts. When dogs eat the seed hulls, they can get an upset stomach
and diarrhea. The real problem is the fungus or mold that attacks
walnuts after they get wet (from rain or sprinklers), which produces
toxins. If the fungus or mold is ingested by your dogs, they can become
very ill and possibly die. Signs that should alert you to walnut
poisoning are vomiting, trembling, drooling, lack of coordination,
lethargy, loss of appetite, and jaundice indications such as yellowing
eyes and gums. Severely affected dogs can produce blood-tinged vomit or
stools. Dogs can take several days to exhibit serious signs of illness.

The above is from an excellent article on common foods that are harmful to dogs.
Read more here ..    

Http://lacetoleather.com/fataltodogs.html