“Gah!” Euryale stormed toward her sister. Percy took the opening. He grabbed Stheno’s platter, scattering poisoned Cheese ’n’ Wieners, and slashed Riptide across Euryale’s waist, cutting her in half. He raised the platter, and Stheno found herself facing her own greasy reflection.
“Medusa!” she screamed.
Her sister Euryale had crumbled to dust, but she was already starting to re-form, like a snowman un-melting. “Stheno, you fool!” she gurgled as her half-made face rose from the mound of dust.

The Son of Neptune, Chapter I