The animal who has "territorial rights" (first claim) can usually pull rank on the one who doesn't. We had a pet squirrel, for instance, and he lived mostly indoors but he liked to go outside too, when we would take him to our country place. Only problem was, the squirrels who inhabited the grounds there would drive him off their territory. He quickly decided that HIS territory included the back porch, however, and he would drive them off that if they dared come too near it. Since the wild squirrels had never really bothered to include the back porch in their official holdings, they were quite intimidated and they would back off at once...but they held unquestioned sway over the garden.

The White Rat had obviously established territorial rights over the workplace, and thus had the confidence to defend it effectively. (And he also had backup...his human friend...and that would increase his confidence.)