Electric "shepherd" for worms

Cross-curricular topic
I once conducted an electrochemistry workshop for students. They enjoyed the experiment with an electric "shepherd" for earthworms, particularly those who went fishing. It was winter, so I went to a fishing tackle shop and bought live earthworms. The subject combines chemistry, biology, and physics, as well as the psychology of behavioural conditioning.

Instructions:
Put an earthworm on a cold copper sheet. The worm will attempt to crawl away from the cold surface. When one end of it moves onto the galvanised sheet while the rest of its body remains on the copper, it will experience an electric shock, similar to cattle or sheep fenced with an electric "shepherd," and will quickly return to the copper. After a few such attempts, it will stop trying.