Is your Yorkie tongue flicking? Is he a male? My male Yorkshire Terrier does that when he is with a female that is in heat. When he first meets her, he holds his head high and catches a scent on the wind, and then stick his tongue out to pick the scent.
Why is Your Yorkie Tongue Flicking?
Your Yorkshire Terrier is doing this for many reasons but the most common one is a dental issue.
I recommend checking his mouth for any visibly damaged or cracked teeth. Abscesses can also cause this, but cannot be identified by merely looking.
A foreign object lodged in her throat or mouth can also be a culprit. Check her mouth to make sure no external object like trash etc. got into her mouth.
Sticking her tongue out and then pulling it back in, can be a clear sign of an upset stomach, or a feeling of nausea. This breed of dogs is known for having indigestion and digestion issues. You could tray a forth of a tablet of 10mg of Pepcid for a couple of days and see if that helps.
Lastly, some focal seizures can cause “fly licking” or “fly biting” where the dog opens and closes their mouth as if they are catching a bug (neurological issue). If you’re sure its not a dental issue than I suggest you have your vet take a look into her teeth.