YouTube user AmmarZed posted a freakish clip about a week ago, titled “Very Fresh Fish.”
The fish is not that fresh, in fact it's already been chopped, but you can distinctly notice it moving around while it's on ice, on the supermarket stand. It has also been gutted, cut in half and has no head attached to its body.
Although it would be easy to assume we have a zombie fish on our hands, there is, in fact, a reasonable, scientific explanation for this phenomenon.
Said answer comes from user mcopleyumd, who explains that adding salt on fillets will let you achieve that effect on several types of fish.
"Basically as long as it has not been fully filleted all you have to do is apply some salt to the meat. The salt acts to refuel the sodium channels in the fish's muscle and allows it to spasm like that," he or she comments.