When Bilbo rejoins the group of dwarves, they ask him how he escaped, and he is keen to tell them everything he experienced. He tells them how he was separated from his companions, and how he arrived in Gollum's cave. He tells them how he escaped Gollum and came to find himself with his friends once again. However, what he does not tell Gandalf and the dwarves is perhaps the most important part of the story: the One Ring. In the cave, Bilbo finds a golden ring; this ring belonged to Gollum (he called it his "birthday present"), but the ring, which is sentient in a way, deserted Gollum to be found by Bilbo. This ring has many powers, including turning its wearer invisible, which is how Bilbo escaped the caves and snuck past Balin to rejoin his friends. Bilbo didn't want to tell his friends about the ring because he wanted to keep it a secret for the moment.