Corn cobs are very tough and hard to chew, meaning they can remain relatively unchanged for a long time in a dog's stomach. The corn cob will pass through the dog's stomach to the small intestine, where they are likely to get stuck.  This is usually an emergency situation because the corn cob obstruction will not pass by itself. If the corn cob remains in the dog's stomach without treatment, it can make him seriously ill.  Always contact your vet if you believe that your dog has eaten corn on the cob.