After the verbs hū 'to sacrifice' and others there is ślu elision of the vikaraṇa śap -- kartari śap [[3.1.68]].,
These verbs belong to the Juhotyadi class. जुहोति 'he sacrifices' 7.1.10. श्लु causes the reduplication of the root. So also बिभेति 'he fears.' निनेक्ति from निज् 'to purify, he purifies.',