The Brāhmaṇadhammika (Snp 2.7) is a powerful and distinctive narrative that tells of the decline of the brahmins and the origin of the sacrifice. It shares something in common with the sprwaling mythic narratives of the Digha, but is much more focussed.
The Buddha is asked by some senior brahmins whether their contemporaries maintain the traditions of old, and the Buddha says no. This is in line with his position elsewhere, where he tends to treat the current brahmins as lesser sons of greater fathers. Sometimes, on the other hand, he dismisses the traditions altogether, arguing that even the composers of the Vedas knew nothing.
The description of the brahmins of old is similar to that found in, say, the Aggañña Sutta. For example, it’s emphasized how they did not store food but relied on alms. This allows the Buddha to position his own followers as “more brahmin than the brahmins”.
According to the story, they used to practice the brahmacariya for 48 years. This is evidently a reference to an early idea about the stages of life that was later codified. The notion appears elsewhere, where the term komarabrahmacariya appears (an5.192:5.4), evidently having the sense of “celibacy since youth” i.e. “virginity”. Komara is added in brackets here, a very unusual intrusion in the text. It’s probably inserted from the commentary by parallel with the prose. Nevertheless, it seems the sense is justified.
This text is that it adopts the point of view of the brahmins and their values in a way that’s understandable given the context, but nonetheless can seem jarring. The Buddha, listing what he appears to be endorsing as the good practices of old, refers to the brahmins not marrying outside of caste, or avoiding sex during the “infertile period”. (I have discussed this in more detail here.) This tendency becomes especially strong at the end when the Buddha is said to describe them as having “fallen away from the doctrine of caste” (Jātivādaṁ nirākatvā). I don’t know, it makes me a little uncomfortable.
Moving on, there are a few mistakes in earlier translations. Seeing as someone recently asked about Ven Thanissaro’s translations, I’ll include them here to see what turns up.
In verse 16 we find Kiccākiccesu, translated by Norman as “what was to be done and what was not to be done”, by Bodhi as “what was to be done and not done”, and by Thanissaro as “what should & shouldn’t be done”. But this is an idiomatic phrase of a kind not uncommon in Pali. Phalāphala means “all kinds of fruit”, bhavābhava means “all kinds of rebirths”. Kiccākicca likewise means “all kinds of business”, as is clear from cases such as Thag 16.10:20.2. Here’s Pārāpariya’s rather memorable description of the monks of his days.
Bhesajjesu yathā vejjā,
In medicine they are like doctors,
kiccākicce yathā gihī
in business like householders,
Gaṇikāva vibhūsāyaṁ,
in makeup like prostitutes,
issare khattiyā yathā.
in sovereignty like lords.
At Snp 2.7:18.4 there’s an interesting line used to describe the houses of the wealthy:
Vibhatte bhāgaso mite
Neatly laid out in measured rows.
Elsewhere the same phrase is used to describe the gates of hell. (an3.36:16.2). Evidently the Buddha was no great fan of the suburbs.
At Snp 2.7:20.1 it says that the brahmins fooled the kings with new scriptures. The Pali verb is gantheti (“have tied”), which in later use literally means to “write a book” (i.e. a grantha). The usage here in this sense is unusual, and I think it’s earlier than any other case. The commentary is highly polemical and says they deliberately composed new scriptures.
But I’m not 100% sure that the text justifies this. I wonder whether it could mean “selecting” passages, i.e. “making a compilation”. We know that this is a very common if not normal practice.
It’s a lot easier to select some amenable passages to support your case than it is to create a whole new scripture. It’s hard work! You have to compose the lines, organize it, make it appear authentic, and co-ordinate all this among a group of like-minded co-conspirators.
Reading it as “compiling” rather than composing is both more historically plausible and gentler on the brahmins.
The root that makes sacrifice possible is the king’s excessive wealth. The underlying psychology is that inequality breeds jealousy and corruption. The king is encouraged to “burn off” his wealth in a display of conspicuous consumption.
This is, in fact, a legitimate anthropological theory of the origin of sacrifice (or at least one of them). In Melanesia, for example, the villages would have a “big man” who over time would gather greater shares of the village wealth, primarily pigs. At a certain point it would become unmanageable; what do you do with so many pigs? So they’d hold a great feast to which neighboring big men would be invited. It’d be an occasion to assert dominance and expand circles of influence.
The specifics of the sacrifice vary from place to place, but there must always be one thing that they share: someone has too much stuff and something has to give.
The text says that the brahmins had the king sacrifice “many hundreds of thousands” of cattle. No doubt this is an exaggeration, but it’s not as unbelievable as it may sound. Sacrifices on this scale have been performed in modern times.
We educated moderns may see talk of animal sacrifice as a peculiar, alien, or primitive rite, but it is still an ongoing reality in much of the world. The Buddha’s movement to stamp it out is still in progress.
I confess, I get a little teary at the climax of this sutta, the thought of the poor gentle cows being slaughtered for no reason. 
The Buddha depicts the brahmanical deities as being outraged by this, roaring out adhamma! “It’s against the Dhamma!”. Norman has “(this is ) injustice!”, Bodhi “How unrighteous!”, Thanissaro “An injustice!”. None of these, I feel, capture the force of the original. I have:
At that the gods and the ancestors,
with Indra, the titans and monsters,
roared out: ‘This is a crime against nature!’
as the sword fell on the cows.
