Some scientists decided to do the following experiments on a dog.
For the first experiment, they cut one of the dog's legs off, then they told the dog to walk. The dog got up and walked, so they they learned that a dog could walk with just three legs.
For the second experiment, they cut off a second leg from the dog, then they told the dog once more to walk. The dog was still able to walk with only two legs.
For the third experiment, they cut off yet another leg from the dog and once more they told the dog to walk. However, the dog wasn't able to walk with only one leg.
As a result of these three experiments, the scientists wrote in their final report that the dog had lost it's hearing after having three legs cut off.