I used to win all the arguments in my shower. Then my girlfriend decided I could wash her hair. I haven't won a single argument since. But I do know that you use your knuckles on the scalp and not your fingernails.
No, No weird fingernails. We just exfoliate with sponges. She feels that knuckle or fingertip massage increases the blood flow. I don't argue. She said "Could you use your knuckles or fingertips?" and I said "You better believe it.."
Learning purposes, obviously.