But I feel it in my bones that this place will be attacked again. Smaug knows now how I came down to his hall, and you can trust him to guess where the other end of the tunnel is. He will break all this side of the Mountain to bits, if necessary, to stop up our entrance, and if we are smashed with it the better he will like it.”

“You are very gloomy, Mr. Baggins!” said Thorin. “Why has not Smaug blocked the lower end, then, if he is so eager to keep us out? He has not, or we should have heard him.”
“I don’t know, I don’t know—because at first he wanted to try and lure me in again, I suppose, and now perhaps because he is waiting till after tonight’s hunt, or because he does not want to damage his bedroom if he can help it—but I wish you would not argue. Smaug will be coming out at any minute now, and our only hope is to get well in the tunnel and shut the door.”
He seemed so much in earnest that the dwarves at last did as he said, though they delayed shutting the door—it seemed a desperate plan, for no one knew whether or how they could get it open again from the inside, and the thought of being shut in a place from which the only way out led through the dragon’s lair was not one they liked.

Chapter 12 Inside information