Okay, so about a month ago I re-watched that movie and had a very similar thought! It's totally adorable--and believable, too! I can completely buy that Sherlock's 221B might have a little, er, mouse problem, with all the stuff they have lying around. And of course Basil wouldn't stand for Sherlock's name to be tarnished! Maybe they could have witnessed the cameras being put up, too. :)