On the way back from detention, Harry hears the voices again.
Harry follows them along the walls until he runs into Ron and Hermione. Of course, they didn't hear the voices either.
When Harry hears the voices again, he runs off after them and the three friends come to a hallway that's flooded with water. There they see spiders crawling out a window and notice a message written in blood on the wall—"The Chamber of Secrets has been opened. Enemies of the Heir, beware."
What the what?
But that's not all. Hanging on the wall from her tail is Mr. Filch's cat, Mrs. Norris.
Suddenly, it seems like every single Hogwarts student empties into the hallway at once and sees Harry standing there by Mrs. Norris. Draco Malfoy starts throwing around slurs again. Mr. Filch is ticked. And everyone seems to think Harry is responsible.
Dumbledore calms the situation down and sends the crowd away. Mrs. Norris isn't dead. She's just been petrified. She can be cured eventually with the Mandrakes in Professor Sprout's greenhouse. (Hey, we just learned that in Herbology!)
But Harry doesn't tell any of his teachers that he heard voices. Ron and Hermione assure him he made the right move.
Hearing voices is just weird and the last thing you would want is to seem weird when you've stumbled across a petrified cat and an ominous message written in blood, right?