Bilbo tries to stealthily walk towards the Arkenstone without drawing attention, but Smaug moves, and the Arkenstone falls further down the pile of gold coins, causing the Hobbit to run after it. "Did you think I did not know this day would come? That a pack of canting dwarves would come crawling back to the mountain", Smaug continues moving around, causing Bilbo to fall down the heap of gold coins. 

Outside, the dwarves hear and feel the rumblings from inside the mountain. "Was that an earthquake?", Ori asked. "That, my lad, was a dragon", Balin slowly answered him. 

Maleficent was about to say something, until an earthquake-like shake manifests, causing the house to rumble. Bard makes it back inside the house, right after it stopped.