The affix ṭak comes after the verb han 'to kill' when the object is in composition with it as its object is hasti 'elephant' or kapāṭa 'gate' and when the sense indicated is that of power.,
This sutra applies where the agent is a human being. As हस्तिनं हन्तुं शक्तः = हस्तिघ्नः मनुष्यः 'a man who is strong enough to kill an elephant'; so also कपाटघ्नः 'a burglar' (who is capable of breaking open the doors).
Why do we say 'where power is indicated'? Observe विषेण हस्तिनं हन्ति = हस्तिघातः 'who kills the elephant by poison'. Here the affix is अण्.,