Someday (but really never) I'll write the definitive study of dogs in Tarkovsky. Of course there's the dog in the famous last shot of Nostalghia. But the dog in Stalker is in more scenes.
Another thought on Stalker. Forget personality tests, forget the opinion of friends and colleagues. Worthless! The world learns something genuine about your personality when it discovers whether or not you laugh when the phone rings in The Zone.