[Bilbo] must stab the foul thing, put its eyes out, kill it. [Gollum] meant to kill him. No, not a fair fight. He was invisible now. Gollum had no sword. Gollum had not actually threatened to kill him, or tried to yet. And he was miserable, alone, lost. A sudden understanding, a pity mixed with horror, welled up in Bilbo's heart: a glimpse of endless unmarked days without light or hope of betterment, hard stone, cold fish, sneaking and whispering. All these thoughts passed in a flash of a second. he trembled. And then quite suddenly in another flash, as if lifted by a new strength and resolve, he leaped. (5.119)

[Gollum] was anxious to appear friendly, at any rate for the moment, and until he found out more about the sword and the hobbit, whether he was quite alone really, whether he was good to eat, and whether Gollum was really hungry. Riddles were all he could think of. Asking them, and sometimes guessing them, had been the only game he had every played with other funny creatures sitting in their holes in the long, long ago, before he lost all of his friends and was driven away, alone, and crept down, down, into the dark under the mountains. (5.22)

[Bilbo] knew, of course, that the riddle-game was sacred and of immense antiquity, and even wicked creatures were afraid to cheat when they played at it. But he felt he could not trust this slimy thing [Gollum] to keep any promise at a pinch. (5.68)