The affix ṇamul comes after the roots naś 'to destroy' and vah 'to carry' when the words jīva 'life' and puruṣa 'person' expressing the agent of these verbs, are respectively in construction with them.,
Thus जीवनाशं नश्यति = जीवो नश्यति 'perishes, so that his life perishes i.e. dies away'; पुरुषवाहं वहति 'the man carries, i.e. the man becoming a servant, carries another on him = पुरुषः प्रेष्यो भूत्वा वहन्ति ।
Why do we say 'when denoting an agent'? Observe, जीवेन नष्टः 'destroyed by life'; पुरुषेणोढः 'carried by a man'.,