This mechanism was designed to be small and compact and resemble the function of a moving jaw. By pulling on a string that was connected to a lever that hung inside a body of plastic it enabled the jaw to move up and down.
The string was connected to a small fish shaped object. When the string is relaxed the fish shape object is almost inside the sharks mechanical mouth. But when the fish shape connected to the string is pulled the string then becomes tense. In reaction to the tense string the jaw lever is lifted and makes the shark mouth close/bite.