Complex sentence: Only the captain's hat is seen for a few seconds, and then a shark pops out of the water and almost eats the mouse, who is is shark white and frantically runs into his hole and shuts the door.
Split into simpler sentences: Only the captain's hat is seen for a few seconds, and then a shark pops out of the water and almost eats the mouse. Jerry is stark white and frantically runs into his hole and shuts the door.