He called the collie’s attention to his friend’s performance to see whether he too was aware of anything standing there upon the carpet, and the dog’s behaviour was significant and corroborative. He came as far as his master’s knees and then stopped dead, refusing to investigate closely. In vain Dr. Silence urged him; he wagged his tail, whined a little, and stood in a half-crouching attitude, staring alternately at the cat and at his master’s face. He was, apparently, both puzzled and alarmed, and the whine went deeper and deeper down into his throat till it changed into an ugly snarl of awakening anger.