 He or she must get trained. It's not cute when dogs bite. Whether the teeth are small or large, they can hurt. Even if your little dog never bites somebody, there are a myriad of other extremely unattractive behaviors that are consequences of not training that little dog. You know, I run into this all the time. Well, it's a chihuahua. It's a schnauzer. It's a poodle warren. It doesn't need training. It's not a doberman, a shepherd, or a rottweiler.