Not to scare you all but this could be a sign of a neurological problem!
Brooke was diagnosed with GME, an inflammatory brain disease and that is one of the symptoms of it. The look like they are licking the air, or catching flies or just looking up at nothing. But, they are also ataxic (wobbly), have a head tilt, or are weak on one side, and many more symptoms. All your dogs probably just have a funny habit....but I wanted to throw this out there, in case you have other symptoms.