In the online video, Japanese diners can be heard screaming when the raw fish starts to wiggle its fins and then miraculously tries to leap off the edge of the plate.
At the end of the clip, the fish makes one more attempt to escape before the cameraman runs away scared and shuts off the footage.
One explanation for why the fish moved may be in the soy sauce.
According to National Public Radio, “Because this (fish) was just killed, its muscle cells were still intact and operational. A live (fish) moves by sending an electrical command from its brain to its muscles. The commands say ‘contract’ or ‘relax.’”
Since the fish’s brain was no longer operating, it couldn't send signals. Salt acts as a substitute. And soy sauce is rich in salt. It caused the muscle cells to react.
"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," NPR reports.