At this point in the adventure, Bilbo Baggins undertakes the most dangerous feat he has been asked to perform. Assuming his burglar role, he creeps down the tunnel and into the dragon's lair. Fortunately Smaug is sleeping, and Bilbo grabs a magnificent goblet to take to the dwarves.
When the dragon senses that some treasure has been taken, he goes on a rampage searching for the thief. After Smaug returns to his hoard Bilbo again approaches to identify himself. The overconfident monster casually exposes his belly, and Bilbo identifies a weakness in a bare patch of skin. As the hobbit exits the den Smaug shoots flames up the tunnel; Bilbo barely escapes. Unfortunately, in Bilbo's banter with the dragon, he exposes Lake-town and its people and accidentally reveals that they helped him. In a rage the dragon destroys the secret entrance and flies off to Lake-town to punish the citizens for aiding the treasure seekers.
This is not my work, all credit for the audio goes to @Bluefax
Image by Chris Rahn, check out his other works at http://www.rahnart.com/