[He doesn't hear anything. Not right away. But he tries to divide his attention, because the others obviously do. He doesn't go on full alert until Percy goes sliding away.
He sends the goat to go chew on vines, and the raptor into the forest - maybe it can find the source. The goat is almost immediately entangled and starts to fall apart. He doesn't have much hope for the raptor. He reaches into his pack for a knife while throwing a wall of earth up to block an approaching vine. Did you know they can go around walls? It catches him on the side instead of head-on, around his arm, yanking him over.]