A sexual position, usually a tight
squeeze (if your with a woman) but if you manipulate the vaginal organs (usually the
clitoris because it's the most sexual stimulant on a woman's body) then the anus, or
asshole, will open up like an umbrella do to the manipulation of the vagina and relaxiation of the woman. That's when you sneak one inbewteen the cheekys my fellow brothers.
With some tedious
finger and licking action to my
girl's pussy, her ass opened up faster than an umbrella on a down poor but closed like a
bank's vault when I inserted my purple helmet warrior. She no longer wanted anal after that.