There are quite a lot of difference between cats and dogs but one of them has just came to my attention: 

Dogs are able to actively interact with the outside world almost exclusively by using their snout while cats can do this by using almost their entire bodies: they play with their paws, rub their sides against things, they bite…

Take a look at this short clip. To me it was almost tragic to see how the Doberman had nothing but his teeth at his disposal when trying to express his ‘feelings’!