Snape’s sneered warning came an instant before the hissed “Legilimens!” There was no time for Harry to prepare, just as the man had intended all along. The professor’s irritation at the task he’d been set combined with his overwhelming dislike of the student with whom he was being force to work had the irate man throwing out the spell with far more force than was necessary or even advisable. A trained occlumens would’ve had trouble resisting the force behind it. Snape expected to find himself immersed in the brat’s thoughts. He never expected an occlumency shield to rival his own.