From 11:00PM PDT on Friday, July 1 until 5:00AM PDT on Saturday, July 2, the Shmoop engineering elves will be making tweaks and improvements to the site. That means Shmoop will be unavailable for use during that time. Thanks for your patience!
Mrs. Norris is Filch the caretaker's cat (and only friend). Her lamp-like eyes in the dark and Filch's habit of calling her "My sweet!" (25.71) both remind us a little bit of Gollum in Lord of the Rings. But J.K. Rowling swears that she hasn't read Lord of the Rings since she was twenty and it's not one of her favorite books (source), so maybe we're imagining the resemblance.