Some people break their necks and can't move their arms because they don't get the call from their brains anymore. We make things to help them move their arms again. We put little boxes on their arms that give small shocks (it doesn't feel bad) to make their arms move again. Computers help us to find the best time to give the shocks by listening to other parts of their bodies, so the shocks come at the right time. Sometimes it works well and the people can use their arms again, and sometimes they still need help from other people.