There are all kinds of urination positions man's best friend takes, including "the squat-raise (most common), squat, arch-raise, combination and handstand," a 2004 scientific study frankly states. The "squat-raise" means the dog squats while slightly lifting her leg, while the "arch-raise" means she arches her back while lifting her leg.
The study found that social functions and proximity to the dog's home influence the ways in which dogs decide to answer nature's call. For example, "females used the squat-raise and arch-raise postures more when off their home area than when on their home area," the study says. "Overall, there was substantial individual variation among females in the postures used while urinating."
But, let's go back to the pressing question: Why, exactly, do some dogs do HANDSTANDS?