Sara's body had excellent reflexes and despite her not being in control at the moment, Mallus was able to make use of them to dodge the knife that was aimed at her shoulder, though it did cause him to lose his telepathic grip on the other boy's neck. And he hadn't expected that boy to come at him with fangs and claws.
This whole situation was fascinating, even when he got nicked by a claw. As the thrown knife clattered uselessly to the ground, he grabbed hold of the one with claws and fangs and bodily tossed him into the other one, intending to knock them both to the ground.