Complex sentence: The shark chases Nancy down towards the sea floor at high speed, but, while Nancy pulls out of the dive at the last moment, the shark continues to dive and impales itself on some rebar sprouting from of the buoy's concrete anchor.
Split into simpler sentences: The shark chases Nancy down towards the sea floor at high speed. At the last moment, Nancy pulls out of the dive and the shark impales itself on some rebar sprouting from of the buoy's concrete anchor.