The fist slides in past the sphincter, which then contracts with relief down around the wrist of the fister. The fistee feels the whole bulk of the hand lodged both painfully and arousingly in her rectum begin to shift, as the fingers unclench to writhe like so many worms deep within her ass. Lots of lube was obviously used here, and the fistees anus is showing absolutely no signs of strain. In fact they both have quite relaxed and serene looks on their faces. I think that they are pros at this. I wonder if taking a fist up your arse can ever just be another day at the office? And what a journey to make it so!