Dogs do it. Cats do it. But humans don’t push their heads against other heads, lean in and simply rub. Not enough. I can easily imagine a world where head-to-head rubbing is an acceptable child-to-grandparent or colleague-to-colleague greeting. Yes, there’s something moose-on-moose about it, but whether forehead to forehead in the kitchen or sideways at the movie theater, hair-to-hair stirs something in the place hugs settle.