While there are any number of foods involving cephalopods in one form another, this particular Japanese squid dish is not what it seems. When you pour soy sauce over the squid, its legs begin to move and “dance” around.
Apparently, the soy sauce is what makes the food get up and dance. There’s some disagreement on Reddit about what exactly is going on, but all agree that the high salt of the soy sauce is key. Here’s a sample of the discussion, from user stumblejack:
This is due to the salt in the soy sauce. The same thing would happen if you poured salt grains on the squid.
It doesn’t “activate the neurons.” Sodium potassium pumps create an action potential.
Edit: To clarify, sodium potassium pumps maintain the ion gradient across the membrane in a living organism. In this case, however, the ion gradient does not need to be maintained. The gradient is created upon addition of the soy sauce which adds sodium ions on the outside of the membrane. Naturally, these want to diffuse across the membrane to try to reach a state of equilibrium between the inner and outer sections of the membrane. So, this has less to do with the pumps than it does with a concentration driven gradient of sodium ions from the outside to the inside.
Whatever is going on here, it certainly is weird as all get out.