Dear Francis,
Any time a dog threatens to bite, it should be taken seriously. Most threats are one part of a pattern of aggressive behavior. If the issue isn’t addressed, chances are high that it will continue and gradually become more frequent and more intense. Behaviorists recognize biting as one aspect of aggressive behavior and have discovered that it can be caused by a wide range of underlying motivations. The most common reason is fear. If your dog is uncomfortable around a person, even if it’s a family member, they may resort to biting to drive off someone they view as a threat.
Things to look for that signal fear in dogs include trembling, lowering the head, tucking the tail between the legs, panting, and a high-pitched bark. Be aware, though, that often the signs of fear are subtle and difficult to notice. Many times they are also combined with threats such as baring the teeth, snarling, growling, or raising the hackles (the strip of fur along the spine). In some cases a fearful dog will just be tense and give almost no warning before lunging and biting.
If your dog is fearful of a person, then the first thing to do is not allow him to run loose around the person. Don’t give him a chance to hurt someone. Keep him on a leash held by an adult, in a run, or in a separate room. Avoiding problem situations will not solve the issue, but in the short term it will prevent your dog from reinforcing the unwanted, negative behavior. The fewer opportunities your dog has to threaten or bite, the lower the chances that he will learn to use biting to get out of a situation that makes him nervous.
For more information on ways that fearful biting can be controlled, see the discussion of treating fearful biting.
* Special note: I also recommend checking up with your veterinarian to rule out any underlying physical issues (e.g., pain).
