A note on the 3xE explosions: I think it may be related to the pigs wearing Santa hats. I've noticed interesting effects sometimes happen around them. For instance on several levels I noticed the momentum of my bird would increase if I passed through their hats just right. And on level 1-15 if I lob a bird in the far right chamber at an angle such that the pig in there starts rolling to the side, he will explode violently. Nowhere near as large as the one in 1-7 though--he usually only takes out one or both of the small pigs next to him if they are still alive at that point.