fisting

I've only had it done twice...The first was with the kinkiest guy I've ever been with. I really enjoyed it. So I asked my new big cock bootie call to give it a whirl...he did a great job and it felt fabulous. Looking forward to more!
 
What is fisting exactly? I'm imagining a man putting his fist up my vagina. Is time taken to open it up? Does it go back to its original size? IF not, why would a woman want that done to her?
 
I did it to a chick on the only one night stand of my life. Probably the reason I never had another one! LOL