In "Fahrenheit 451," who is the mascot of the fire department?

The mascot of the Fire department in "Fahrenheit 451" is the mechanical hound.  This "dog" is used for sniffing out offenders and has the ability to kill people who are hiding illegal books.  The hound has a needle in its nose and the needle is full of poison. 

The mechanical hound begins to take an interest in Montag and when Montag comes to work the hound stalks him and acts like he is going to inject Montag with poison.  Montag talks to Captain Beatty about the problem and he promises to fix the hound, but nothing changes.  Montag gets very nervous and uncomfortable around the hound.  We learn that Montag is indeed hiding books and the hound can detect the fear in Montag.