Who is Sunny Baudelaire from The Reptile Room and what is their importance?

Sunny is the youngest of the Baudelaire children. Her favorite pastime is biting things, and her talents with her teeth are very useful at various times throughout the story. Sunny's new friend is the Incredibly Deadly Viper. He bites her in the beginning of the story, and she bites him back, an act that forges a strong friendship between the two.