http://imgur.com/gallery/fDrwryE

He seems to enjoy it.

had a Greyhound (Sid) years ago who would get savage with "the other dog" (his reflection in the tinted glass of the media centre ). He would snarl and growl and of course this "other dog" would snarl and growl back. Sid was an alpha dog and would not tolerate this "other dog" not submitting to him. It took him a long time to figure out the "other dog" was not a threat

Hey, if it worked once it'll work again. Unless he's just 'tarded in that lovable dog way my guess is he sat licking the window once, the owner gave him what he wanted (getting inside), and it clicked that that's how you get attention when you want to be indoors. Dogs are like that.

Or the window tastes like whatever he ate last time he licked it.

Our dog works the back door like a boxer on a speed bag. FAST, both front paws. There's no paint left. LOL Fortuntely it's a steel door.

The comments under that video are priceless!