Why does electricity hurt?
Electric current is the flow of incredibly tiny particles called electrons. This flow of electrons is called electric current. Electric current is always going right back where it came from, in kind of a circle.
Electrons are always anxious to get home (maybe mom has cookies and milk waiting). That's why the outlets in the wall at home have three holes for the electric plug connection. One for the electrons to come out, one to go back in, and another one for an extra way home in case they get lost (that may sound weird, but it's true).
There are two ways electricity can hurt you:
First, it can burn you very badly. Although electrons are tiny, there are zillions of them, and together they can pack quite a punch. If the electrons are flowing through a conductor such as copper wire, they're pretty happy, because the wire is easy to get through it offers little "resistance" to the flow of electrons.
On the other hand, if the electrons are trying to get through something more difficult, like your arm for instance, they have to try harder. In the process of trying to get through your arm, they create heat. Electron heat is not a good thing to have in your arm or anywhere else in your body for that matter.
Only materials called insulators can stop the flow of electricity. These materials are important to remember because they can help stop the flow of electrons into your body.
Second, electrons can interfere with your heart, making it beat incorrectly, or not at all. You see, your brain tells your heart how fast to beat by sending it electrical messages, called "impulses." Your heart can't tell the difference between the good impulses from your brain and the bad impulses from the wire, and it gets confused. And you really don't want your heart to get confused. That would be a bad thing.
So, it's very important to keep your body away from electrons when they're on the way home. And, remember, they're always on their way home!