Bilbo discovers a hole in the on smaugs lef breast as bare as a snail of of it's shell

Hollow or patch would be the answer. 

" He saw a large patch in the hollow of his left breast as bare as a snail out of its shell. "

The man in the village goes on top of the tower, nd get's his father's acient bow arrow and shoots. landing right in the spot. He saved the village and the darfs keep the treasure and it results in the elves coming because they want treasure too. Any ways it turns into a war against the elves, men adn dwarfs.
hope this helps and I can recall this by memory! XD I hope i can get a for this because i actully did just remember this!