This is the process of inserting a whole hand and arm into the anus (much like fisting) when the hand and indeed first is far enough up. the anus - the person can then rapidly open and close the fist- thus making a flicking motion and taping the spleen.

This is said to be enjoyable and sexualy arounsing.

When you eat dirt for the first time and leave your family to build a shack in the woods