Montag is suspicious of the Mechanical Hound when it targets him as he tries to pet it.
The Mechanical Hound is pretty creepy. It is much more than just a searcher. It is one of the book’s many paradoxes, because it is both alive and not alive. It also sort of does not seem like a hound, because it has eight legs, making it more like a spider!
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.
It is also described like a bee, because it has a needle of poison. Montag is “fascinated” by the creature that he describes as a beast. However, it is a fascination driven by fear.
When the Hound tries to attack Montag one day when he starts to pet it, Montag is frightened. The hound is “suspicious” of him. He tells the other men that the Hound doesn’t like him. The other firemen scoff at the idea.
"Come off it. It doesn't like or dislike. It just `functions.' It's like a lesson in ballistics. It has a trajectory we decide for it. It follows through. It targets itself, homes itself, and cuts off. It's only copper wire, storage batteries, and electricity." (Part I)
Montag is worried that someone knows he has stolen a book, and that is why the Hound is targeting him already. He reminds the others in the firehouse that the Hound can be programmed. Beatty responds by asking him if he has any enemies. Montag is beginning to worry about the path he has chosen, a path that deviates from his society’s values and puts him at risk.
This incident foreshadows the danger that Montag is in when he steals the book. As a fireman, he has access to books. Books are illegal though, and he is always in danger that someone will suspect him. Will his colleagues, and even the Mechanical Hound, someday find out his secret? Montag wonders about his blind acceptance of his society’s ways ever since his conversation with Clarisse, but taking the book is his first open act of defiance.
From there, there is no turning back. Whether or not the Hound knows, he will not be able to keep his secret forever. Eventually he will have to go on the run, and the Hound will be hunting him for real.
In addition to a society that relies on television instead of books, the Mechanical Hound is a monster that demonstrates another of Bradbury's warnings about technology in the future. Here we have a drone-like killer robot that will target anyone without regard to the person's actual true guilt or innocence. This creates a real reign of terror, perfect for an oppressive dystopian society.