Excess saliva is called DYSPHAGIA and there can be a number of causes, but it's mostly due to an inability to swallow the saliva. Extra saliva can be stimulated by smell. There was a study of fragrances and their use in fast food. If I remember correctly, it was McDonald's that relies mostly on the fragrances of beef flavored oils that are sprayed on their french fries to make the customer more hungry so that they will buy more food (it has been found that TASTE is actually stimulated by SMELL as we eat because the odor from the mouth leaves the mouth, travels over the lips and enters the nostrils). So, most likely, any excitement of the nerves stimulates extra saliva.