Blood bending

Bloodbending is subskill of hydrokinesis or what we call Waterbending.Bloodbending does not necessarilly bend blood but instead the water on our muscles ( remember that our body is made of 70% water ) thus enabling advanced waterbenders to manipulate the body of their foes at will. According to hama, waterbenders can only do this ultimate subskill of waterbending when its Full Moon, where the powers of the waterbenders is at its peak.However its unknown if its full moon on the episode southern raiders when Katara uses this skill. Bloodbending is introduced to the series on book three episode number eight "the puppetmaster".