Just like a car battery, the shock collar has negative and positive posts called electrodes that touch the dog.

 For a correction, simply push a button, instead of having to use both hands to jerk on a leash, like the choker or spike collar methods!  The pain of the electric current running through the dog's body punishes them.

 There are 3 major pre-requisites before starting: good batteries, lots of anger, and a good reason ( like a two thousand-dollar item ruined).      

 Imagine finding this item ruined after coming home from an evening out or a hard day's work.  Wouldn't you rather avoid this situation by giving your dog the expert training they need, so they'll know how to behave even when you're not home? 

 This method really speaks for itself.  The ultimate of the 3 levels of pain.