Snake and Lightning

I was never really a big fan of Harry Potter, but I read all the books. :) My favorite book was Prisoner of Azkaban. My favorite HP movie was also Prisoner of Azkaban and the other movie where Harry and Hermione danced (http://www.youtube.com/watch?v=DFe0OR-Vaww) . I thought it was so artsy. Hahaha.

Can you guys guess what’s happening in this illo? :)
Hint: It’s supposedly a magical phenomenon.