No one got it.
I understand that if you have to explain your joke, maybe it's not a very good joke, but bear with me. I think once you get the reference you'll be pretty impressed.
Back in the 80s there was a commercial for a Purina-brand dog food called HiPro. It featured a dog running in the woods and the announcer promised if you fed your dog HiPro, its coat would shine with a "HiPro Glow." The dog then began to glow as it ran through the woods.
Thirty years later Edward Cullen reveals himself to Bella not only to be a vampire, but also discloses the little-known fact that when vampires stand in the bright sunlight, especially after running in the woods, they too have a glow that looks oddly familiar.
But that's not all. Vampires don't just glow. As you can see from this close-up still shot from the film of Edward's frail pale chest, they sparkle in the sunlight.
But hey, what's the big deal. In another shot from the 1985 dog food commercial, Purina reveals to us this is not because Edward is a vampire. It's because he has apparently been eating HiPro dog food.
Poor Purina doesn't get any credit for being the first one to come up with the idea of a wild animal running through the woods and sparkling in the sun. And to add insult to injury, their 1985 sparkling special effects actually look better than the multi-million dollar movie from the next millennium.
So there you have it. And now when Edward and his sparkly head next appears in a theater near you, you can also appreciate the beauty of what is actually the HiPro glow.