First and foremost, I'm going to precede this with the note that I am a witch who works a lot with the concepts of flesh and bone. This is just one step further up the squick track from throwing bones, which I already do. Okay? Okay.
I've felt called to extispicy for a good while now, but it's not the most talked about practice around here, because of thoughts about humaneness and/or convenience. Moreover, I'm unsure I have the guts (heh) to do it; but then, everyone gets a little hung up on aspects of their individual path and I've been pretty much in the clear so far, so perhaps this is it.
Extispicy is the divination of entrails. When called haruspicy, it is a Roman/Etruscan practice traditionally done with sheep liver, but extispicy as far as I'm aware is a more broad term. Since it's my personal preference not to waste anything I'm given, I'll be working with extispicy.
Sources on this are scarce, because no one really practices extispicy anymore, and certainly not in a pagan sense; see "overabundance of love and light," where killing an animal is seen as taboo, even though we do regularly in indirect manners. (Yes, even vegans. This isn't the time for that discussion, though.)
Fortunately, however, this means that almost all sources on extispicy are academic. Which is good for us, because that means the information isn't being fed through a filter of neopagan bullshit.
(Again, sources at the bottom.)
It's been in my thoughts that it might be possible to breed mice. It is common in many older pastoral practices to breed for a ritually pure animal (pure white/black/etc., or similar criteria). Moreover, I am and always have been interested in breeding and genetics.
Were I to breed mice, I would be able to control everything said mouse consumed and the environment it lived in. If I had a longer-term question, it would be possible to push the energy of the question into all of the nutrients it received. This is good because readings are typically done by anomaly. (By the sources, however, it appears that the readings were not done on the assumption that the individual animal was important, but rather that it could be interpreted truthfully by the will of the gods [see Goetze].)
Another benefit of doing this with mice is that they can be more easily humanely killed than, say... a sheep, which I have neither access to nor the willpower to raise or breed.
***Historical notes: it is worth saying that it is probable that this method arose in part because it encouraged people to selectively breed their herds for better traits, as oftentimes the definition of a "ritually pure" animal has to do with color or consistency of coat, temperament, or other such features that one can breed for.***
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Sources I Have Been Able to Access
"The Palace Gate of the Liver: A Study of Terminology and Methods in Babylonian Extispicy," by Ulla Jeyes. A scholarly source from JSTOR. The nature of this source, which includes a lot of Babylonian language, makes it difficult to plunge through, but it is the most comprehensive readily available source on extispicy that I've found to date.
"An Old Babylonian Prayer of the Divination Priest," by Albrecht Goetze. Deals less with interpretation and more with the ritual practice of extispicy, including what I surmise to be cleansings beforehand. Probably should not be used word-for-word, and instead adapted to your individual practice, if used; it deals with Babylonian gods and gathering water from the Tigris and Euphrates, which obviously for many is not an option. I may write an adapted version of this in the future.
"Reading Livers Through Reading Literature: Hepatoscopy and Haruspicy in Iliad 20:469 ff..." by Patrick Hunt and Whitney de Luna. A scholarly and free access! resource from Stanford. Deals less with actual literature and more with archaeological and historical context. A good read and doesn't require an account! Features also other sources in the footnotes for further exploration of the topic.
"Extispicy (or Extispicium)."Â Appears to be a cursory resource. No sources cited, but contains information I have not seen elsewhere in a public source. Use with caution.
"The Image of Heaven: Hepatoscopy, Liver Divination." This is not a primary or scholarly source per se, but rather a proposed method to performing hepatoscopy with a handmade deck of cards rather than an actual liver. Contains some interesting information such as probabilities.
Sources I Have Been Unable to Access
"Mapping the Entrails: The Practice of Greek Hepatoscopy," by Derek Collins. This is an academic, philologic source arguing that the process of hepatoscopy was inherently binary. This is hosted on Project MUSE and as such is not publicly available to unsubscribed institutions.
"Notes on Some Technical Terms in Extispicy," by Ivan Starr. Scholarly source and hosted on JSTOR. It seems much synonymous with a similar source listed above by Ulla Jeyes. I have it downloaded but have not yet looked through it.