Like a shark and a remora
The remora have a symbiotic relationship to the shark. The shark is the apex predator. The remora live off the scraps of kills that fall from the shark's mouth. Remora also groom the shark, including going right into his open mouth to clean up in there, too.
Our GSD is lying on the floor. The Shih-tzu is right next to her. She GSD is C.R.U.N.C.H.I.N.G a rawhide chewie as if it were a bone. Shards of chewie are falling from her mouth. The crunching sound is loud. The Shih-tzu is lying very close to the big one's mouth. She is scarfing up the slivers and scraps. But she is also picking shards off the GSD's lip jowls. In essence, she is cleaning the big one's mouth.
They are an unlikely pair, these two. The GSD is nearly 10 times the size of the Shih-tsu, and yet there they are, side by side. Very closely side by side.
Like a shark and a remora fish.
Only cuddlier. 
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SWEET!
I have been attacked by a remora so be careful 
