They are "busy" to put it mildly, some aren't too hyper, but almost everyone I have come into contact with has been a wallbouncer, totally whacked out. When my old Pit Bull mix was alive, there was a local petstore who's owner had a JRT. He attacked my dog on sight, and luckily for him, he was dragged away in time to prevent any real retaliation. My dog couldn't figure out what he was up to at first, he was pulling hunks of hair out of my dog's neck, and it took my dog about a minute to get angry (And some people think Pits are crazy!) and about the time he had gotten to the point he was about to explain the facts of life to the other dog:
1. I weigh 75 pounds, you weigh 12.
2. I can put your entire head in my mouth and almost close it without hurting you!
3. One of my molars is about half the size of your mouth, and can remove your legs with one bite.
The owner drug him away and he dodged that one. He found out that a Lab is no better than a Pit Mix when he attacked his owner's mother's dog, and she decided to teach him respect. She chewed him up pretty badly and broke several ribs. It didn't phase him, he went after my dog again, but they caught him as he ran to attack. This time, my dog was ready for him. It would have been very bad.