The smallest thing sets anxious Cas off. If he settles for a moment, just the intake of breath from someone is enough to cause him to leap to his feet again. Then he rushes about, mouth wide open, panting.
The Staffordshire Bull Terrier may settle again – briefly. Then a sound from outside starts him off again. When suddenly alarmed, his response may be to charge at somebody, mouth open, and jump on them – usually the young man.