If they do, it could be because they want to feel more like part of the family, or it's just a particular animal's personality and that animal was matched with the person meant for it.
The golden I used to have did similar things w/her ears/eyes when I approached w/a leash. It was a habit formed from years of me sliding a new collar on with the leash attached. She'd squint and pull her ears back in anticipation of the collar being slid over her head.
The smile? I never got that.
