Śrīmad-Bhāgavatam · Text 10.20.9
Who is speaking and story frame
श्रुत्वा पर्जन्यनिनदं मण्डुका: ससृजुर्गिर: ।
तूष्णीं शयाना: प्राग् यद्वद्ब्राह्मणा नियमात्यये ॥ ९ ॥
śrutvā parjanya-ninadaṁ
maṇḍukāḥ sasṛjur giraḥ
tūṣṇīṁ śayānāḥ prāg yadvad
brāhmaṇā niyamātyaye
The frogs, who had all along been lying silent, suddenly began croaking when they heard the rumbling of the rain clouds, in the same way that brāhmaṇa students, who perform their morning duties in silence begin reciting their lessons when called by their teacher.
Read the purport on Vedabase.ioFrom Canto 10, chapter 14 onward, the translation and purports were completed by Śrīla Prabhupāda's disciples after his departure, and published by the Bhaktivedanta Book Trust.