What is the role of the mechanical dog in Fahrenheit 451?

The Mechanical Hound is a destructive, man-made monster resembling a large dog. It is a soulless enforcer that kills thinkers and readers. Unlike the firehouse dog, the Hound does not rescue people. Instead, it either kills them, disables them, or ignores them (even when they are endangered). The Hound is an eight-legged artificial creature capable of detecting and memorizing the scents of up to 10,000 people. A needle bursts from its nose, and the needle is capable of stunning, paralyzing, wounding, poisoning, or killing a victim altogether, depending on which of its various poisons it selects.