Dogs have a natural proclivity to jump on people. How often they do this will vary with breed and personality. It's been suggested that dogs jump up on people to get a better look at someone's face -- not to attack that person, but to interact with him or her. Dogs interact with each other this way, too. Especially if they're of similar breeds, their faces are close to each other and they use their senses of smell and vision to explore.

Most indoor, short haired cats keep themselves clean by regularly grooming themselves with their tongue and teeth.  Long haired cats, outdoor cats, stray cats and cats who get themselves into grease, paint or some other noxious substance can use human help from time to time.  Cats who are regularly bathed also have significantly fewer allergens on their fur, about 40% less, which is a great help to those humans who are allergic to cat dander.