Describe the Mechanical Hound.

From the text:

"The Mechanical Hound slept but did not sleep, lived but did not live in its gently humming, gently vibrating, softly illuminated kennel back in a dark corner of the firehouse. The dim light of one in the morning, the moonlight from the open sky framed through the great window, touched here and there on the brass and the copper and the steel of the faintly trembling beast. Light flickered on bits of ruby glass and on sensitive capillary hairs in the nylon-brushed nostrils of the creature that quivered gently, gently, gently, its eight legs spidered under it on rubberpadded paws."