The affixes ktavā and ṇamul come after the root kṛ 'to make' when an indeclinable word in composition with it and the meaning is the communication of anything in a disagreeable or undesired way.,
The word अयथाभिप्रेताख्यान means literally 'to denote the expression of that which is not really intended' i.e. a manner not suited to the proper communication of that news, such as communicating a bad news in a loud voice and good news in a low voice. The compounding being optional, the affix क्त्वा may be replaced by ल्यप्. Thus we have three forms नीचैःकृत्य, नीचैःकृत्वा, or नीचैःकार. Thus if one had communicated an agreeable news like the birth of a son in a low voice, the other may retort \किं तर्हि वृषल नीचैःकृत्वा, नीचैःकृत्य, or नीचैःकारमाचक्षे\; and so, if one had communicated an unpleasant news as ब्राह्मण कण्याते गर्भिणी in a loud voice, the other may reply \किं तर्हि वृषलोच्चैःकृत्वा, उच्चैःकृत्य, or उच्चैःकारमाचक्षे । (See 2.2.22 for compounding).
Why do we say 'communicating in an undesired manner'? Observe उच्चैःकृत्वाऽऽचक्षे पुत्रस्ते जातः । Here only क्त्वा is added. Why have we repeated क्त्वा in this sutra, when in this chapter, by the rule of वाऽसरूप 3.1.94, ktva would have presented itself in the alternative? The repetition is for the sake of samasa or composition, by the application of 2.2.22. The repetition of णमुल् is for the sake of the subsequent sutras, into which the anuvritti of ktva and namul runs concurrently.,