Moments before the deadly blow. The raised fin is about to come crashing down like a karate chop on a shark (circled). It has been driven to the surface by the orca before this coup de grace
An interesting article on how Orcas track and kill sharks.... check it out, and the other photos. I do think their sheer size difference helps, but I am intrigued how they have learned that holding a shark upside down can immobilize it! Shame that humans have not go th3 ability to do that to sharks when they are attacked!