This cuttlefish is dead. Completely dead.
Its head has been cut off, and it has been served up in a bowl ready to eat. And yet, when soy sauce is poured over the squid, something bizarre happens.
This is an old YouTube video taken in Japan, but it's doing the rounds thanks to a Vine created by SciencePorn, and is so mind-boggling we had to share it again.
According to American radio station NPR, which covered the phenomenon back in 2011, the reaction is due to the high salt content in the soy sauce.
As the squid was recently killed, and its muscle cells are still working, the salt triggers chemical reactions similar to those it used to move its tentacles when it was alive, NPR journalist Robert Krulwich explains:
Blame the soy sauce.
Soy sauce, rich in salt, caused its muscle cells to fire. To get motion, add sauce.
Because this squid was just killed, its muscle cells were still intact and operational. A live squid moves it tentacles by sending an electrical command from its brain to its muscles. The commands say "contract" or "relax." But since this animal lost its head, its brain can't send signals. Salt acts as a substitute.
Extra sodium (the salt) sends ions to the cell that trigger the cell to open up, creating a cascade of chemical activities that causes the cell to fire, so the muscle twitches. That's why the camera person keeps pouring soy sauce on those tentacles.
The same sort of effect can be seen in the legs of recently-killed frogs - shown in this video here using ordinary salt granules: