Just like your dog lying down and being scratched all over ... they enjoy it.
We watch what they do in their play time, and we reward them for doing it. It's pretty much as simple as that, really.
They're what I wake up for every morning and they're the last thing I think about before I go to sleep. I spend more time with these animals than most people spend with their children.
It's basically a leash for a dog or like a bridle for a horse. You can control the elephant just from its head.
It's really similar to dog training, you just have bigger treats.