भीस्म्योर्हेतुभये

After the causatives of the verbs भी 'to fear' and स्मि 'to wonder' even when the fruit of the action does not accrue to the agent the आत्मनेपद is employed, when the fear is produced directly by the causative agent.
The phrase 'of the causative ending in णि' is understood in this sutra and is to be supplied from the previous aphorism. This sutra is also restricted to cases where the fruit of the action does not accrue to the agent. The word हेतु in the aphorism has been defined later on in sutra 1.4.55 (स्वतन्त्र कर्त्ता); it is the agent which is the mover of another's agent. When a fear is caused by a हेतु it is called हेतुभय. The word भय 'fear' in the aphorism is illustrative, and includes by implication विस्मय 'astonishment' also. As जटिलो भीषयते 'the jatila, the cock-headed frightens.' मुण्डो भीषयते 'the munda, the shave-headed frightens '; जटिलो विस्मापयते 'the jatila astonishes,' मुण्डो विस्मापयते 'the munda astonishes' i.e., the very fact of matted-hair or shaven-head frightens,' &c.

Why do we say हेतुभय? For if the fear or astonishment is not the direct result caused by the agent, but arises from something else, then the atmanepada will not be used. As कुञ्चिकयैनं भाययति 'he frightens him with the kunchika,' रूपेण विस्माययति 'he astonishes with his form'. Here kunchika and rupa are the instruments, which cause fear or astonishment, and are not the hetu thereof.