Because the preservation of this working ability is of highest importance to most registered JRTCA/JRTCGB breeders, Jack Russells tend to be extremely intelligent, athletic, fearless, and vocal dogs. It is not uncommon for these dogs to become moody or destructive if not properly stimulated and exercised, as they have a tendency to bore easily and will often create their own fun when left alone to entertain themselves.Their high energy and drive make these dogs ideally suited to a number of different dog sports such as flyball or agility. They may seem never to tire and will still be energetic after their owner has called it a day. While socialised members of the breed are friendly towards children, they will not tolerate abuse even if it is unintentional.