Okay, I'm going to try to explain this the best I can because I don't have a video recorder to actually get it on camera to show you. I think this is a dog thing and not a Yorkie thing, too, because my other dog does it.
Every once in a while, when outside, either one of them will put their nose to the ground really intently. And then all of the sudden, start to rub their cheek on that spot on the ground (butt still in the air). They will either rub from one cheek to the next or slide from cheek all the way to the ground and then turn over on their back and wallow/roll side to side on their back.
I recently saw a video of Guinness doing this on his facebook page (ahem, Alisha). That's exactly the kind of act I'm trying to describe if you see this and want to attach that video here for me
Anyway, I've often wondered what that was all about and why they did that. Then, the other night, I think I figured it out (kind of). It's a smell or a bug that just gets them going. How do I know this? Well, in my living room (remember we live in Alabama), I see a HUGE flying roach (you know the tree ones) crawling across my living room floor in front of the tv. Both of my dogs go over to it and start to paw at it. Then, Mandie starts doing that cheek/wallow on the bug thing. I was so grossed out. She was just rubbing her face all over that stupid roach. ICK! But..interesting still. lol
Just thought I would share my discovery...apparently they like to wallow on bugs. LOL