Sharks are the most perfect killing machines in existence. Luckily they are primitive beings and in addition they are only in the water, confined without having almost contact with the humans beyond a few zones of the planet.
In the tape we see that a kind of meteorite falls from space. He falls into the sea and a hungry shark eats it thinking that it is food. It is not food, but the object does not kill it either.
What it does is to turn the shark into a kind of robot, which eliminates the limitations that these animals have, especially that which prevents them from leaving the water. Now, the shark is a robot and can breathe out of the water.
That will start to persecute people and kill them even out of the water, so now it is a total killing machine, without limitations and with a lot of blood thirst.