He’d only survived this long because the two snake-haired-ladies—gorgons, they called themselves—couldn’t seem to kill him either. Their claws didn’t cut his skin. Their teeth broke whenever they tried to bite him. But Percy couldn’t keep going much longer. Soon he’d collapse from exhaustion, and then—as hard as he was to kill, he was pretty sure the gorgons would find a way.

The Son of Neptune, Chapter I