Mirrors don't have nostrils.
I just noticed this. They don’t appear to have any other opening for air so I guess that means they breathe through their mouths. Both sexes are open mouthed in their official art so I suppose that makes sense. (I guess the one in the header image is holding its breath)
They are also canonically strong runners. Now, one of the biggest concerns with fast moving, active animals is oxygen intake, since you need a lot of it to properly fuel all the muscles. This is actually why cheetahs have relatively small teeth - larger ones would require bigger roots that would take up space used for the nasal cavity.
One can extrapolate from this that Mirror dragons run with their mouths wide open. The beautiful mental image of this is only enhanced when one takes into account their large tongues (which appear to be longer than their snouts). Just picture it. A pack of Mirrors running open-mouthed across the landscape, their tongues flapping majestically in the breeze…
It’s too bad they don’t eat insects because I have to imagine they swallow quite a few on accident.