This could be nasal discharge. Puppies can become infected with kennel cough or other upper respiratory infections. It is also possible your puppy has a cleft palate and food/liquid is draining out the nose. Lastly if this is a very young puppy it could be regurgitation from the stomach if it has been given too much milk. This puppy needs to be examined by a veterinarian. Foamy, white discharge from the nose is not normal.
It's normal don't worry.... Caused by heavy breathing during his walk!
Does it have rabies?
White or green discharge coming from the dogs nose
It has rabies and will soon die. You should probably plan a funeral. It will be a very touching and boring time