If you don't like stray animals, Athens can be a little traumatic at first. On just about every city street you will find some kind of furry creature going about his or her daily business. For the most part these animals are fairly harmless, unless you drive a motor bike, because they love to chase them. While they are harmless, the dogs in particular are not really friendly. While they sometimes follow people around (this helps them navigate the streets safer) many don't like to be touched, and all of them are fairly dirty and infested.
Cats on the other hand are much more the scavengers, with tourists often providing for them. I've seen many a cat use its feline whiles to score a meal or two. They are often more likely to accept a scratch on the head than a dog, but I'm sure they expect a table scrap for this service. As with the dogs, the cats of Athens are also fairly dirty, and if you can't resist giving one a pat, make sure to wash your hands immediately after.