Usually people who like various degrees of pain or something other than typical soft touches will do this for sexual gratification.

It may involve beast bondage with ropes and such, nipple clamps, slapping or whipping the breasts, temporary or play piercing, hot wax, ice cubes, biting and pinching, suction with something other than a person's mouth, electricity with devices meant only for use on the human body, chemical play with substances such as Icy Hot or peppermint oil, and abrasion (sandpaper, brushes, rough fabric, or other textured items).

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