Smaug, the dragon in The Hobbit, boasted to Bilbo about being "armoured above and below with iron scales and hard gems." However, when he displayed his underside for Bilbo's examination, Bilbo discovered a large bare patch of flesh, and thus a vulnerability, in the hollow of his left breast. Bard the Bowman slew Smaug by shooting a black arrow into this hollow.
If you mean when he tricked the dragon into showing him his 'hide' of jewels, he was pleased to see there was one spot that was not covered, and that meant the dragon wasn't completely invulnerable.
Bilbo claimed that under the terms of the contract he was due a proportion of the dragon's treasure, and that he had taken the Arkenstone as his share.
Because Bilbo accidentally made Smaug (The dragon) get angry at them. Their city was destroyed by the dragon and they weren't too happy.
yes because he wants the treasure and to kill the dragon.
Thorin has become affected by 'dragon greed'. Just like Smaug, he is loathe to part with a single coin or cup.
The Thrush tells Bard about the missing spot of armor on the dragon's belly. And the thrush got the information listening to Bilbo tell the dwarves about it.
His stomache was adorned by gold and jewels from laying on them, save for one area which could be a weak point.
He saw a small bare patch. That bit of information is what led to Smaug's death.
Bilbo told Smaug a riddle to keep him distracted.
How it is as light as a feather and as hard a dragon scales
Yes, he does. He flatters the dragon, who shows off his jeweled belly, but there is a missing place.
He noticed that one goblet of his had been stolen.
Bilbo spotted a small bald spot in the hollow of the dragon's arm. He told the dwarves about it and it was overheard by the thrush. The bird later told Bard about it and he sent his black arrow into the spot and killed the dragon.
Bilbo claimed that under the terms of the contract he was due a proportion of the dragon's treasure, and that he had taken the Arkenstone as his share.
The thrush was beating a snail against a rock, and it helped Bilbo figure out how to enter the mountain.
Biblo 'borrows' the Arkenstone.
they left the house and expected bilbo by the green dragon by 11am
No, he makes it back home. After all, he does have a part to play in The Lord of the Rings.