I keep my occlumency shields up all the time in Dark Arts class. Not that I think he's going to try to read my mind anymore. I was afraid he was a legilimens at first, but now I don't think now that he is at all. But it's a way to practise the discipline of keeping them up, and anyway, just in case...

Besides. It makes me a little distracted, and it suited my purposes to be a little less afraid let him think I was sorta dense.