They're All Horror Movies Now

If there's one thing in this world that has cut my productivity in half, it's Netflix's amazingly wonderful Watch Instantly service. And as it has slowly become my primary source of televisual entertainment, I have  grown increasingly mystified and intrigued by its recommendations. You may have to enlarge this screenshot to see what I mean; note the "Recommended based on" square in the lower right corner:

On the one hand, this recommendation is spot on - I loves me some Shakespeare, and this production sounds very promising indeed! But how does it know? I struggle mightily to believe that any algorithm in the world adds Spinal Tap to Monty Python and the Holy Grail...and comes up with Macbeth. Am I forgetting the part where Macduff turns it up to eleven? Is there a deleted scene in which the Three Witches endeavor to buy a shrubbery? These films are not related in any discernible way. And yet, the almighty Netflix computer has used them to come up with a remarkably accurate model for what I will or won't like. Terrifyingly accurate, actually.