Kamasutra 2.4.25

2.4.25

bhavati hi rāge 'pi citrāpekṣā/ vaicitryāc ca parasparaṃ rāgo janayitavyaḥ/ vaicakṣaṇyayuktāś ca gaṇikās tat kāminaś ca parasparaṃ prārthanīyā bhavanti/ dhanur vedād iṣv api hi śastrakarmaśāstreṣu vaicitryam evāpekṣyate kiṃ punar iheti vātsyāyanaḥ//

Here ends the marking with the nails. Marks of other kinds than the above may also be made with the nails, for the ancient authors say, that as there are innumerable degrees of skill among men (the practice of this art being known to all), so there are innumerable ways of making these marks. And as pressing or marking with the nails is dependent on love, no one can say with certainty how many different kinds of marks with the nails do actually exist. The reason of this is, Vatsyayana says, that as variety is necessary in love, so love is to be produced by means of variety. It is on this account that courtezans, who are well acquainted with various ways and means, become so desirable, for if variety is sought in all the arts and amusements, such as archery and others, how much more should it be sought after in the present case.