He (Atri Rsi) began to offer prayers to the three deities, who were seated on different carriers - a bull, a swan and Garuda - and who held in their hands a drum, kusa grass and a discus. The sage offered them his respects by falling down like a stick

Expressions researched:
"Thereafter he began to offer prayers to the three deities, who were seated on different carriers" |"a bull, a swan and Garuḍa" |"and who held in their hands a drum, kusa grass and a discus. The sage offered them his respects by falling down like a stick" |"he began to offer prayers to the three deities, who were seated on different carriers"

SB Canto 4

Thereafter he began to offer prayers to the three deities, who were seated on different carriers—a bull, a swan and Garuḍa—and who held in their hands a drum, kuśa grass and a discus. The sage offered them his respects by falling down like a stick.

SB 4.1.24, Translation and Purport:

Thereafter he began to offer prayers to the three deities, who were seated on different carriers—a bull, a swan and Garuḍa—and who held in their hands a drum, kuśa grass and a discus. The sage offered them his respects by falling down like a stick.

Daṇḍa means "a long rod," and vat means "like." Before a superior, one has to fall down on the ground just like a stick, and this sort of offering of respect is called daṇḍavat. Atri Ṛṣi offered his respect to the three deities in that way. They were identified by their different carriers and different symbolic representations. In that connection it is stated here that Lord Viṣṇu was sitting on Garuḍa, a big aquiline bird, and was carrying in His hand a disc, Brahmā was sitting on a swan and had in his hand kuśa grass, and Lord Śiva was sitting on a bull and carrying in his hand a small drum called a ḍamaru. Atri Ṛṣi recognized them by their symbolic representations and different carriers, and thus he offered them prayers and respects.