Does your dog bite?

This's the question a kid asked me the other day being in the school's entrance. It seems to be a polite way to say: Can I stroke your dog? Obiously, most people will answer: Of course my dog doesn't bite. It sounds so ridiculous to my ears! Why don't you ask directly to the dog? How can people know if their beloved pet is gonna bite you? It not depends on me, we cannot have any control over animals although we think the contrary.
If my dog considers you a threat he will try to defend himself with tooth and nail. I'd like to have a white shark instead of a tiny dog, most likely they don't try to touch it!