The sword Bilbo finds in the trolls’ cave in J.R.R. Tolkien’s The Hobbit is Sting.
After the trolls are turned to stone, Bilbo and the Dwarves discover weapons in their hoard. Bilbo takes a small Elvish blade and later names it Sting after using it against giant spiders in Mirkwood.
Sting glows blue when Orcs or goblins are nearby. This feature helps Bilbo and later Sam recognize danger, and it gives the sword an importance far beyond its small size.
The blade was made in Gondolin during the First Age. The same hoard contains Glamdring, which Gandalf takes, and Orcrist, which Thorin carries. Sting’s short length makes it suitable for a Hobbit, although Tolkien often calls it a sword rather than a dagger.