Silent Sprint is a power-up for Sly Cooper in "40 Thieves" in Sly Cooper: Thieves in Time. It costs 1000 coins and is available after completing "Open Sesame." Rioichi Cooper has this as a default ability.
This power-up allows Sly and Rioichi to sprint (hold while moving) without alerting any guards. This also adds a motion blur effect to the sprint animation.