Haha! An explosion of Sperm Whale! I love how the guy stops for a second, as though he hears something. I can only imagine his internal monologue before making that last cut.
So why did this happen? Well when animals die, the little creatures that make a home inside them live on; namely the bacterial organisms and enzymes that inhabit the gut. These little bacteria go to work digesting the internal organs, which creates gas as a by product of this decomposition. Essentially this sperm whale, which had been sitting on the beach for some time, had turned into a 35 ton, decomp gas filled ballon. The Whale carcass was under a great deal of pressure, which this guy released in an explosive fashion with his rather large knife.