There were other and more interesting things, moreover, which had caught Chum’s attention. The sounds and scents from the wagon’s unseen interior carried to him a message of fear, of pain, of keen sorrow. Chum had half-risen, to investigate. Link, noting the action, had signalled the dog to lie down again. And Chum, as always, had obeyed. But now, through his sullen brooding, pierced a sound that set every one of the collie’s lively nerves aquiver. It was a hissing whistle—broken and staccato. It was a signal Link had made up, years ago—a signal which always brought the dog to him on the gallop. For that signal meant no summons to a romp. It spelled mischief. For example, when cattle chanced to stroll in from the highway, that whistle signified leave for the dog to run them, pell-mell, down the road, with barks and nips—instead of driving them decorously and slowly, as he drove his own master’s cows. It had a similar message when tramp or mongrel invaded the farm. At the sound of it, now, Chum was on his feet in an instant. He found himself confronting the obnoxious stranger, who was just reaching forward to clutch him. Chum eluded the man and started toward Link. Shunk made a wild grab for him. Chum’s ruff—a big handful of it—was seized in the clutching fingers. Again sounded that queer whistle. This time—thanks to the years of close companionship between dog and master—Chum caught its purport. Evidently, it had something to do with Shunk, with the man who had laid hold on him so unceremoniously. Chum glanced quickly at Link. Ferris was grinning. With an imperceptible nod of the head he indicated Shunk. The dog understood. At least, he understood enough for his own purposes. The law was off of this disgusting outlander. Ferris was trying to enlist the collie’s aid in harrying him. It was a right welcome task. In a flash, Chum had twisted his silken head. A single slash of his white eyetooth had laid open the fat wrist of the fat hand that gripped him. Shunk, with a yell, loosed his hold and jumped back. He caught the echo of a smothered chuckle from Link and turned to find the Ferrises and the child surveying the scene with happy excitement—looking for all the world like three people at an amusing picture show. The dog catcher bolted for his wagon and plunged the lacerated arm into the box beneath the seat. Thence he drew it forth, clutching in his hand a coil of noosed rope and a strong oversized landing net. “Tools of his trade!” explained Link airily, to his wife and Olive.