Why Is My Dog Foaming At The Mouth?

My dog has started foaming at the mouth whilst playing with a ball/stick. It doesn't happen at any other time and it has only occurred in the last 6 months (he is 6 years old). Everything I have read on the internet relates to parvo or rabies but I don't believe it's that serious as nothing else about him has changed. (Jacqui Norman - South Australia)

This type of foaming at mouth is quite common and is normally a result of the dog's state of mind rather than what they are playing with. Some dogs show this phenomenon when excited, scared, or stressed. Others show it as a sign of heat stroke from lots of running around. In most cases it disappears when the strong inducing element stops and is nothing to be concerned about. If however your dog shows these symptoms in one particular field or location then it could be something more obscure, such as a reaction to a specific vegetation or smell.