One year in New York City, warts arrived in the park with a vengeance. Dog owners were finding weird gray, often pea-size growths, usually on their dog’s face and inside his mouth, on his tongue and lips. (These are not contagious to humans). These basically harmless annoyances (unless the dog gets so many that they interfere with eating, which is rare) disappear in a month or two once the immune system mounts a defense. After that, the dog is immune to new outbreaks. But, while immune, the dog can still be a carrier. Always talk to your veterinarian if you have concerns.