Galvani in the 1700s famously showed that a dead frog can be made to twitch by electric stimulation. The hind legs are particularly susceptible. Salt helps in the activation, as shown in these videos: https://www.youtube.com/watch?v=sJifWqUa2pY https://www.youtube.com/watch?v=2YZJt_Bw3eo Can the same be accomplished with a fresh dead fish? Fish are more easily available for demonstrations to children. Have you tried this, and if so which part of the fish is most readily stimulated?