The anunāsikā is optionally the substitute of an aṇ vowel which occurs in a Pause, and is not a parigṛhya,
अ, इ and उ, short and long, may, when final in a Pause, be pronounced as nasals, provided that they are not Pragrihya 1.1.11 &c.) The अण् here is a Pratyahara with the first ण् ॥ Thus दधिँ or दधि, मधुँ or मधु, कुमारीँ or कुमारी ॥
Why do we say 'of an अण् vowel?\ Observe, कर्तृ, हर्तृ ॥
Why do we say 'which is not a pragrihya'? Observe अग्नी, वायू which are pragrihya by (I. I. 11).,