© Best Life
Each individual human being has its own unique odor, and dogs can smell all of them. A dog’s sense of smell is 10,000-100,000 time stronger and better than ours, and because of that, they can smell things we could never realize they exist.
So we can agree that dogs have way more information about other people than us. In fact, dogs can even tell between the scents of identical twins that consume the same diet and live in the same environment, and amazingly, dogs can even smell illnesses before doctors can diagnose them.
Anyway, if your dog starts growling at someone out of nowhere, then he probably smelled something and perceived it as something negative, like fear or a strange dog.