i've had some personal experiance with fisting, the trick is
1)major fore-play
2)lube, but if used proporly, not as much as people think
3)start with just 1 or 2 fingers thn work your way up
4)When you decide to go for it don't actually make a fist. Bring all of your fingers to a point and enter that way.

P.S. once you get in, dont get overexited and start hammering away at her. It won't take much to bring her to orgasm.

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