Having assumed this wonderful python's body, he (Aghasura) spread his mouth like a big cave in the mountains and lay down on the road, expecting to swallow Krsna and His associates the cowherd boys - SB 10.12.16

Expressions researched:
"Having assumed this wonderful python's body, he spread his mouth like a big cave in the mountains and lay down on the road, expecting to swallow Kṛṣṇa and His associates the cowherd boys"

Srimad-Bhagavatam

SB Canto 10.1 to 10.13

After thus deciding, that crooked Aghāsura assumed the form of a huge python, as thick as a big mountain and as long as eight miles. Having assumed this wonderful python's body, he spread his mouth like a big cave in the mountains and lay down on the road, expecting to swallow Kṛṣṇa and His associates the cowherd boys.

SB 10.12.16, Translation

After thus deciding, that crooked Aghāsura assumed the form of a huge python, as thick as a big mountain and as long as eight miles. Having assumed this wonderful python's body, he spread his mouth like a big cave in the mountains and lay down on the road, expecting to swallow Kṛṣṇa and His associates the cowherd boys.