Some dogs are very destructive with their toys. Even dogs that are generally pretty good can be VERY destructive sometimes.
This can be a very annoying behavior if you are the dog owner buying the toys they destroy. What is equally annoying is that many dogs quit playing with their toys after they get the squeaker out or the toys quit squeaking.
Why do dogs do this?
One theory goes back to nature. When dogs hunted for prey, they would hunt and kill. Their prey would squeak or make noises.
This was part of their natural hunting instinct. Once caught, the prey made noises as the dog proceeded with the kill, which can be very satisfying to a hungry dog. When the prey was dead - the squeaking stopped. A squeaky toy can give a dog the same type of satisfaction.
-From the Petplace.com