But what the hell is pony-play?

I was over at Samhain checking out the new releases, when this caught my eye:

Warning: This title contains the following: explicit sex, anal sex, bondage & discipline, pony-play.

Yippee, all of my favourite subject matters in one book.

I’m guessing this is a sexual act, but I find myself feeling quite disturbed, when trying to imagine what the logistics could be.

Anybody?