You can think of all the things that dogs can get into either inside the house or outside. My sister’s dog got hold of a frog the other day, put it in his mouth and then spat the frog out. She made sure the frog was okay, but the dog started foaming at the mouth, spitting and all that. They got really scared and called the emergency room. They said, “Oh, the toad probably got scared and urinated in the dog’s mouth. That’s what caused the foaming.” I have known snakes that secrete a substance that makes a dog foam at the mouth after they touch them, not poisonous snakes, but worms, garter snakes or grass snakes. When dogs get hold of them, they sometimes foam.
Certain substances they get hold of in the environment – for example dirt – will sometimes cause them to foam. You can also get something similar to foam, but it’s really just hyper saliva. Some dogs when they get nervous will spit more than usual. I’ve seen dogs come into the vet clinic and they’re really nervous and they want strings of saliva. I’ve seen other dogs think they’re going to be fed treats and that gets their salivary glands going. They will either have strings of saliva or foam or blow bubbles. They spit a little extra because they are waiting for the treat you are going to give them.
Puppies are the worst at foaming at the mouth. Many times they swallow what comes into their mouths. Older dogs seem to have a little more common sense. Many times they will taste something that is poisonous and they will spit it out.
Sometimes foaming at the mouth can really be benign. Most of the time, there is something in their mouth that irritates the mucous membrane. So if your dog is foaming at the mouth, don’t think of it as a mad and raging psycho dog, it’s simply something they tried to taste or play with that caused it.