This is Alan Rickman reciting Shakespeare's Sonnet 130, about how beautiful his mistress is. And who should she be but Hermione? The background Musica is "The Maid With the Flaxen Hair" da Claude Debussy.
I'm an unabashed Snape/Hermione 'shipper, so I just had to make a video about them! Of course, one wonders if any of this really happened, o was it all Snape's lustful fantasy...
