Śatapatha Brāhmaṇa ("of a hundred paths") 6.2.2.22

6.2.2.22

yadvevopāṃśu | reto vā atra yajña upāṃśu vai retaḥ sicyate vapā paśupuroḍāśo haviretāvānhi paśuḥ

And, again, why in a low voice;--there is seed here in the sacrifice, and seed is cast silently--the omentum, the animal cake, and the chief oblation, for of that much consists the animal sacrifice.