The pups start to grow very quickly. Once the puppy reaches this age you can really begin to enjoy the experience of hand raising them . The chances of them dieing is greatly reduced. They are starting to regulate their own temperature and can pee and poop without your help.There is alot of sensory development at this stage.Negative experiences can have a negative effect on their personality at this age. At 4 weeks the puppies show their fun side they enjoy playing with each other. They learn social interaction at this stage. They learn bite inhibition. That is why if a puppy is taken away from its littermates too soon it will have alot of social problems training issues etc. The puppy teeth will appear at around 5 to 7 weeks. At 4 weeks you can introduce the puppy to puppy chow.