While traversing soft snow without any special gear, you slip. Should you slide facedown or faceup, and why?

If you are on a slope you should go face down and dig your toes and fingers into the snow if the slope is steep enough to get into an uncontroled slide. If you happen to have an ice ax you hold the top with one hand and hold the handle across your chest and put you weight on the head of the ice ax to dig the sharp point into the ice/snow. Look up ice climbing

The best way to fall in soft snow is face down at which I mean face towards ground, but facing up to protect your face. If I was falling, I'd try use the body's three points of contact. The upper portion of your back followed by your hip and hopefully you'll stop yourself with your feet which are together. Good Luck!

You question reads as though you already knew the answer, but I agree with the last guy. You don't slide on your back because you lose the use of arms and legs, plus if you hit rocks or sharp objects you risk damaging your spine. Afterall, getting hit in the groin maybe the least of your worries if the slope is seriously steep.