Leo's Map of Monsters: The Spitfang Lizard by Kris Humphrey
It's Leo's job as the Guardian's apprentice to protect the village from the monsters that lurk in the surrounding forest. Whenever a monster gets too close to the village walls Leo must venture out, using his magical map to first find the monster and then do battle with it. In this book, Leo must track down a deadly Spitfang Lizard before it reaches the village. He is given one piece of advice-first they spit, then they bite. If a Spitfang's throat swells up . . . run!