Kamasutra 2.7.9

2.7.9

utsaṅgopaviṣṭāyāḥ pṛṣṭhe muṣṭinā prahāraḥ//

Blows with the fist should be given on the back of the woman, which she is sitting on the lap of the man, and she should give blows in return, abusing the man as if she were angry, and making the cooing and the weeping sounds. While the woman is engaged in congress the space between the breasts should be struck with the back of the hand, slowly at first, and then proportionately to the increasing excitement, until the end.