When one keeps animals, whether for pets or exhibits, one is responsible for keeping them fed and healthy.
At the Dahlem Center, we have several turtles, a couple frogs, and two snakes currently in our collection. All these animals are obligate carnivores - they must eat other animals. One of the things we keep on hand to feed them is goldfish. Another is crickets.
Yesterday Mark was feeding the masses yesterday afternoon just before closing, and I was able to capture the action with the larger of the two garter snakes.