The theory behind mild shock is that your dog only needs a little stimulus to get his attention and stop barking. Intense shock theorists believe that some dogs are too stubborn to respond favorably to a little zap and need a much stronger to be trained. The progressive stim Best Rechargeable Bark Collars ulus type of shock collar stems from the theory that the technique of gradually increasing shock output from a barely noticeable stimulus through increasing levels works faster, and more effectively in training your dog, because your pet is given a chance to notice that each time he barks the stimulus intensifies, instead of receiving a nuisance shock that doesn't deter his barking, or instantly being traumatized by an intense shock.