make sure it's LESS than 30 mg , make sure it has food , DO NOT GIVE aspirin to ANY puppies r small dogs, otherwise call your vet...
Check the dogs stools to see if it passed. Perhaps you can still salvage it.
Take it to the doctor and get an X-ray, see if the mouse had a disease.
first,see how the dog is doing then take it to the vet if it has any weird things
Obviously if the dog swalloed the rock, it was small enough not to be a problem, if he swallowed it and u think it may be big enough to cause damage to the throat or stomach, consult your vet.