Did you know that in language, there is a classroom that can only be opened with all 3 colored keys, red, blue, and black? There are 3 overlapping doors with yellow, blue, and red handles. It leads to a useless classroom with nothing interesting except flipped and stacked desks and chairs. Hardly anything useful except a few generic items. I only checked it in little puss mode, maybe there's something more interesting in it during the chase modes. When you reach the 2nd half of the level (the area past the server room and the gross pizza room) look for a single door with a yellow handle and have all 3 colored keys with you (not counting the history level's forest key). It's one of those classrooms with only one way in and out.