Thanks for the tip, Touchwood. 

I was practicing making an entire body out of one cube, sans the head and hands, and when it got down to the wrists, one half of the arms  in that area are lower than the face on the other half (sort looks like the wrists have super hero claws). I wanted one flat faced surface when I go to add the hands for an easy bridge so thought I'd just drag and weld the verts on the longer part backwards.