The affix ṇamul comes after a root daṃś 'to bite' preceded by the preposition upa when a word ending with the Instrumental -3rd case is in composition with it..,
The Upapada samasa is optional in this case 2.2.21. Thus मूलकोपदं शम् भुङ्क्ते or मूलकेनोपदंशम् भुङ्क्ते 'he eats after having relished the food with radish'. Similarly आर्द्रकोपदंशम् भुङ्क्ते or आर्द्रकेणोपदंशम् 'relished with ginger'.
The words मूलक &c in the above examples are the 'objects' of the verb उपदंश्, and 'instruments' of the verb भुज् ।
By the rule of वाऽसरूप (III. I. 94) the affix क्त्वा (or its substitute ल्यप्) may be optionally used, wherever we may use the affix णमुल् । Thus मूलकेनोपदश्य भुङ्क्ते ।,