Double strike
From Guild Wars Wiki
A Double strike is a form of attack of Assassins, which means to strike with both daggers at once. The chance of performing a Double strike with a normal attack is increased by 2% with each rank in Dagger Mastery, and by 50% by the Critical Strikes Elite skill Locust's Fury. Dual Attacks automatically double strike, while all other attack skills are incapable of double striking.
