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Sting!
The sword that is affectionately known as Sting has a magic property, it glows blue when enemies are near. We know that because in 'Lord of the Rings' Frodo has it, and it does indeed glow blue when enemies are near, like in the Mines of Moria. However, during the Orc attack on the cliff at the finale of the movie, Sting doesn't glow at all