After the animals, the zoo key was the favorite part of going to the Philly Zoo for me and my three daughters, Yakira, Margo and Dalia, into the 1990s. They would fight in the car on the way to the zoo over who got to carry it first. When we entered the zoo there was a giant map with all the animal locations and which animals had a zoo key story machine.  Then we would go from machine to machine, put the key in, turn it, and the machine would talk about the animal for thirty seconds or so. You learned the difference between Indian and African elephants, for example. A bunch of the machines were inevitably broken, so part of the fun was predicting whether a given machine was going to talk or not. This made for a fun surprise every time it did talk. On the way home the kids would argue over who got to keep the key until the next visit.