504
Śrīmad-Bhāgavatam
[Canto 3, Ch. 13]
PURPORT
It appears that great hills and mountains also have their roaring power because they are also living entities. The volume of the sound vibrated is in proportion to the size of the material body. While Brahmā was guessing about the appearance of the Lord's incarnation as a boar, the Lord confirmed Brahmā's contemplation by roaring with His gorgeous voice.
TEXT 24
ब्रह्माणं हर्षयामास हरिस्तांश्च द्विजोत्तमान् ।  
 स्वगर्जितेन कक्रुमः प्रतिस्वनयता विभुः ॥२४॥
brahmāṇam harṣayāmāsa 
    haris tāmś ca dvijottamān 
    sva-garjitena kakubhaḥ 
    pratisvanayatā vibhuḥ
brahmāṇam—unto Brahmā; harṣayāmāsa—enlivened; hariḥ—the Personality of Godhead; tān—all of them; ca—also; dvija-uttamān—highly elevated brāhmaṇas; sva-garjitena—by His uncommon voice; kakubhaḥ—all directions; pratisvanayatā—which echoed; vibhuḥ—the omnipotent.
TRANSLATION
The omnipotent Supreme Personality of Godhead thus enlivened Brahmā and the other highly elevated brāhmaṇas by again roaring with His uncommon voice, which echoed in all directions.
PURPORT
Brahmā and other enlightened  brāhmaṇas  who know the Supreme Personality of Godhead are enlivened by the appearance of the Lord in any of His multi-incarnations. The appearance of the wonderful and gigantic incarnation of Viṣṇu as the mountainlike boar did not fill them with any kind of fear, although the Lord's resounding voice was tumultuous and echoed horribly in all directions as an open threat to all demons who might challenge His omnipotency.
TEXT 25
निशम्य ते घर्घरितं स्वखेद- 
    क्षयिष्णु मायामयम्बकरस्य ।