अथ यां तृतीयां जुहुयात्तां जुहुयादपानाय स्वाहेत्यपानस्तृप्यति ॥ ५.२१.१ ॥
atha yāṃ tṛtīyāṃ juhuyāttāṃ juhuyādapānāya svāhetyapānastṛpyati || 5.21.1 ||
1. When he [the eater] offers the third oblation, he offers it saying, ‘Apānāya svāhā’ [I offer this as an oblation to apāna]. With this, apāna becomes pleased.
Atha, next; yām tṛtīyām juhuyāt, when he offers the third [oblation]; tām juhuyāt, he offers that; apānāya svāhā iti, [with the mantra] ‘Apānāya svāhā’; apānaḥ tṛpyati, [then] apāna is pleased.
Apāna is the aspect of the vital force responsible for elimination of waste from the body.