Smell is a very important sense for a puppy. When they are born, their eyes are closed, so they must instinctively rely on their sense of smell to survive. Being able to smell its mother for nourishment as well as comfort is key. As your puppy matures, smell plays a different roll. Smells help to identify people, places, objects, other animals, etc.
Taste is just as important as smell.
For puppies, knowing the taste of its mother's milk is key for survival. A dog will rarely eat anything that doesn't entice his sense of smell. However, there is a dog or two or three out there that will eat just about anything. Touch refers to the puppy s willingness to be touched by people. Some puppies withdrawal and have the same reaction as they grow older while other puppies and dogs react positively when touched.