They also have can see a wider space then humans can. Dogs are of the few animals that keep playing when they are grown. Puppies chew on slippers because they are growing new teeth and it is also a form of play. Some dogs like some people more then others, if a person is relaxed, they will maybe like that person. If someone is afaid of dogs and walks backward, or walks in jerky movements the dog may not like this person, or maybe even attack.
Puppies also go pre-hunting.