How does Gandalf trick the trolls in The Hobbit?
Gandalf tricks the trolls by impersonating, or mimicking, the other trolls' voices. By pretending to be William, Bert, or Tom, he stirs up conflict with the other trolls, making them argue and forget their original purpose of killing and eating their captives. Gandalf's clever trickery distracts the trolls enough that they do not realize that dawn approaches, and when the sun rises, the trolls immediately turn to stone, thus freeing the dwarves and Bilbo. This humorous scene serves multiple purposes in the text: 1) Tolkien injects humor into what could be a frightening scenario; 2) Tolkien also builds on his characterization of Gandalf as a very clever and quick-witted guide.