A thrush of an ancient and magical lineage contributes greatly to the success of Thorin and his associates in The Hobbit by J. R. R. Tolkien.
The first thing that the thrush does is to help the band in opening the door. Thrór's Map stated that the magic keyhole could be unlocked on a specific day when the thrush knocked. Thus when the thrush cracked snails, making a knocking noise, Thorin knew that it was the right time to open the door.
Next, the thrush overheard Bilbo talking about the one area in which Smaug was vulnerable, a bare patch on his breast missing the protective armor covering the rest of his body. The thrush carried this news to Bard, who spoke the language of the thrushes. Bard, an expert archer, killed Smaug by firing an arrow at that bare spot on the basis of the information conveyed by the thrush.