After the blow at Vritra Indra hides, and the gods send Vayu as the swiftest to see whether the enemy lives. His price is the first vashat of King Soma. He reports Vritra dead; the gods seize him (the text treats him as Soma) in cups, but he is putrid, and Vayu blows him sweet in return for having the vessels named after him. Indra then buys into the cup by promising that speech will be intelligible, claims half, is given a quarter by Prajapati, and in return limits intelligible speech to the fourth that men speak.
The gods cannot agree who shall drink Soma first and run a race for it. Vayu leads, then Indra, then Mitra and Varuna, then the Ashvins. Indra, seeing Vayu will win, asks to share: an equal share is refused, a third is refused, a fourth is granted. Indra and Vayu win together, and the cups are drunk in the order of finishing. The text adds that Bharata charioteers claim a fourth of booty on this precedent.
What is different here:
A race, not a scouting errand. No Vritra, no putrid Soma, no Prajapati and nothing about speech; the quarter is bargained for during the race.
The gods ask Vayu to help them slay King Soma. He chooses a boon: his cup shall be drawn first. Soma, slain, turns putrid; Vayu sweetens him for a second boon, that the vessels be called his. Speech once spoke without distinction; the gods ask Indra to make it distinct, and his boon is that the cup be drawn for him and Vayu together. It is drawn once for Indra and twice for Vayu because Vayu chose two boons.
What is different here:
No Vritra and no scouting: Soma himself is slain. Indra earns his share by dividing speech and there is no quarrel or judge. Adds that spoiled things are hung in a windy place because Vayu purifies.
The hymns state the privilege without a story: Vayu drinks first, has none before him, and takes the first draught as his portion; Indra rides beside him as charioteer.
What is different here:
Only the fact of the first draught; no explanation of how it was won.
Sources: The Satapatha-Brahmana, tr. Julius Eggeling (Sacred Books of the East 12, 41); Rigveda Brahmanas: the Aitareya and Kausitaki Brahmanas, tr. A. B. Keith (1920); The Veda of the Black Yajus School (Taittiriya Sanhita), tr. A. B. Keith (1914); Hymns of the Rigveda, tr. R. T. H. Griffith (1896), hymns read for the Vedic layer