ramrods, it was steadily pacing backwards and forwards in a narrow
space, uttering, as it did so, those curious little guttural sounds of
pleasure that only an animal of the feline species knows how to make
expressive of supreme happiness. Its stiffened legs and arched back made
it appear larger than usual, and the black visage wore a smile of
beatific joy. Its eyes blazed magnificently; it was in an ecstasy.

At the end of every few paces it turned sharply and stalked back again
along the same line, padding softly, and purring like a roll of little
muffled drums. It behaved precisely as though it were rubbing against
the ankles of some one who remained invisible. A thrill ran down the
doctor's spine as he stood and stared. His experiment was growing
interesting at last.

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.

Then the doctor called to him in a tone of command he had never known to
be disregarded; but still the dog, though springing up in response,
declined to move nearer. He made tentative motions, pranced a little
like a dog about to take to water, pretended to bark, and ran to and fro
on the carpet. So far there was no actual fear in his manner, but he was
uneasy and anxious, and nothing would induce him to go within touching