@Rhea it makes them more sensitive. Any bit of skin that has a small layer removed, like when cuts turn to scars and such the area will be more sensitive to the touch. Apparently it's something people do with their nipples... also may be tmi but when babies breastfeed, if the child is tongue tied or just not used to latching then they can actually break skin on the mum's nipples and they can become more sensitive. Idk why it is, but it is what it is... what they're doing just have some sort of similar effect, as much as it makes me feel queasy every time they do i🥲.