This video appears to show a fried fish flapping around like it's still somehow alive. The video went viral on Weibo, after being recorded in Hengyang, Hunan Province, in southern China. 

As much as it's distressing to watch, and maybe one of the least appetizing things you'll ever see, there is one thing to be grateful for: The fish is definitely not alive. Keep it in mind as you watch that the fish isn't feeling any pain.

So what's happening? 

Well, in other viral videos that have done the rounds lately, the movement comes from a chemical reaction that stimulates the fish's muscle tissues. 

For some time after death, muscle motor neurons within these tissues still have some membrane potential. The fish's brains are very much dead, but most of their tissue is very much alive. The muscles in the fish contain adenosine triphosphate, the main source of energy for muscle contractions.

"Most of the tissue... is actually still alive," a chemistry professor at the University of Virginia explained to Discovery News. "Cell metabolites are nearly intact, membrane voltages or potentials that exist in nerve cells are probably still close to intact."

"Even though the brain function is missing, the tissues will still respond to stimuli."

Adding salt to the fish (in the form of table salt or soy sauce) can trigger muscle spasms in very recently deceased fish and cephalopods. The salt gets absorbed and changes the voltages across nerve cell membranes, triggering the (somewhat violent) contractions of the muscle you see in most viral videos.

However...

In this video, the fish's flesh appears to be cooked. Once it's been cooked, the muscles won't contract like this in response to salt, no matter how fresh it is. It's possible the heat is contracting the spine or flesh in some way (the way fish or meat will curl when you put it into a hot pan).

Or, it's possible the fish isn't as cooked on the side we don't see. The fish is still dead, and has just been fried on one side. The other side isn't, and they're using the salt trick to make it twitch from that side.

Or it's possible the whole thing is a hoax, being pulled off with pieces of thread. Which one do you think? Any other explanations?