Answer:
Bilbo regains consciousness in pitch black. Crawling along the tunnel, he picks up a metal ring, “almost without thinking.” Taking comfort from the discovery that his little sword is also an elvish blade that shines when goblins are near, he starts walking down the tunnel but stops when he walks into cold water.
When Gollum can’t find his ring, he guesses (correctly, this time) that Bilbo has it and comes to attack Bilbo. As Bilbo runs away, he puts his hand in his pocket to figure out what he does have there, and the ring slips onto his finger. Gollum runs past, and Bilbo follows Gollum to the “back door.” There Gollum stops, smelling many goblins, and blocks the passage. Eventually, he senses Bilbo and readies himself to spring. Bilbo briefly contemplates killing him, but a “sudden understanding, a pity mixed with horror, welled up in Bilbo’s heart,” and he jumps over Gollum instead.
Bilbo runs to the door and is seen by the goblins because the ring has slipped off his finger. He puts it back on, dodges goblins, and eventually squeezes through the door, leaving “his nice brass buttons” all over the doorstep.
