Nah it's easy Steve. You hold a small shaving mirror in your hand, turn your back on the big mirror and look at your bum/rear view quite clearly.

I expect the lassie was chuffed to have so much of her bottom out for viewing. That's the 'If you've got it flaunt it' brigade's philosophy.
It was a very nice bum. Mine would cause riots in the street, armed response Police rushing to the scene and people fleeing to safety.

I wonder what Jesus really did wear? Sandals are mentioned in the Bible. People were forever washing eachother's feet, and no socks seem to have been in evidence.