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A puppy is a baby dog, generally less than one year of age. The term is sometimes abbreviated to pup, and in that form is used for the young of some other animals, such as the wolf. The number of puppies in a litter varies greatly by breed. Some smaller dogs typically bear only one or two puppies at a time, while some larger breeds bear a dozen or more. In some cases, one puppy will be the runt of the litter, being noticeably smaller than the others.
Born after approximately 63 days of gestation, puppies emerge in an amnion which is bitten off and eaten by the mother dog. At first, puppies spend ninety percent of their time sleeping and the rest feeding. Puppies develop very quickly during their first three months, particularly after their eyes and ears open and they are no longer completely dependent on their mother. Puppies are highly social animals and spend most of their waking hours interacting with either their mother or littermates. It is important that the puppy receive regular positive socialisation with other dogs and humans during the first sensitive period (eight to twelve weeks).