" Now that it’s an emergency, Snape and Harry snap immediately into Legilimency. They know how to do this. For good measure, Snape protects their communication against detection by either Umbridge or Voldemort by presenting an outward show of dislike for Harry while, incidentally, warning everyone else that Umbridge is capable of poisoning students. "

― Lorrie Kim , Snape: A Definitive Reading