What Makes an Animal Treif

Shechita done perfectly does not settle whether an animal may be eaten. An animal can be slaughtered flawlessly and still be treifah — carrying a defect, disease or damaged organ that makes its meat forbidden.

Chazal enumerated seventy kinds of treifos in an animal and seventy-two in a bird. Any one of them disqualifies it.

Why almost none of them is checked

Seventy defects sounds like an inspection nightmare, and the resolution is the most important structural point here.

An animal slaughtered properly stands in a presumption of permissibility. There is no obligation to check for the treifos generally — only where something raises a concern. The default is that the animal is fine.

That is why a kosher abattoir is not performing seventy examinations on every carcass. It is relying on a presumption, and looking where the presumption is weak.

And why the lung is the exception

One organ is exempted from that default. The lung must be checked in animals, even where nothing has raised a concern.

The reason is not anatomical importance. It is frequency: defects that render an animal treif are simply common in animals' lungs. So the presumption of permissibility does not carry there, because the thing it assumes to be rare is not rare.

This is the paradigm case of miut hamatzui — a minority common enough to require checking — and the lung is the example the poskim reach for when defining the category elsewhere, including for insects in produce. One definition offered puts miut hamatzui at "close to half", precisely by reference to lung adhesions.

The practical consequence is a rule with teeth: after slaughtering an animal, its meat may not be eaten until the shochet has checked the lung and established its status.

This is also where the term chalak — glatt, "smooth" — comes from: a lung found free of adhesions. Which adhesions disqualify, and which may be tested or removed, is the shechita house's determination and not a judgement to make at a counter. The word is also used more broadly as a marker of standard: one source uses it of meat that was properly soaked rather than merely rinsed within the three days.

Birds you open at home

Poultry bought whole is the case where the checking falls to you. On opening the bird, examine the internal organs — liver, heart, spleen and lung — for anything that would render it treif: that they are not abnormal in their nature, and that there is no perforation or defect of any kind.

And the instruction attached to that is explicit: anyone not expert in this must ask a rav about any doubt that arises. This is not a category to resolve by looking it up.

What to bring to a rav rather than judge yourself:

• An internal organ missing, doubled, eaten away or decayed.
• Any change in an organ — a liver dry and crumbling, dissolved, or changed from its natural colour.
• A bird's lung blistered, swollen, or with flesh unlike its nature.

One case is not a question but a prohibition: a bird found with reddish, foul-smelling fluid in its cavity carries a concern of danger and is forbidden.

Broken bones, and the test that dates the break

Some fractures render an animal treif — but only if they happened during its life. A bone broken after shechita is no problem at all.

So where a break is found and nobody knows when it happened, there is a physical test:

A femur head dislocated from its socket raises the same question — whether it came out during life — and goes to a rav.

Tzomes hagidin

At the leg joint there is a bundle of sinews called tzomes hagidin — three in an animal, sixteen in a bird.

If those sinews were damaged, or even one of them severed, the animal is treif. And if the bone opposite them is broken, it is treif on the concern that the sinews were damaged. Any case where the area is injured or swollen goes to a rav.

Three modern cases

These are worth knowing because they arise from ordinary farming practice rather than from injury.

Vaccination in the leg. Birds injected at the joint, at the tzomes hagidin, where the site has swollen — the bird is treif. In doubt, or where there is a wound or a bite from another animal, ask a rav.

Vaccination in the neck. A bird injected in the neck raises the concern that the oesophagus was perforated, which would render it treif. This needs a rav.

Force-fed ducks. Birds fattened for their livers are fed through the oesophagus, and the feeding device can damage it. They are fit for kosher shechita only where the shochet checks the oesophagus afterwards and finds it undamaged.

Two things that disqualify before shechita

An animal mauled by a predator is treif and may not be slaughtered at all. So where predators are known in the area, this has to be established beforehand rather than discovered later.

A hole in the skull renders a hen or an animal treif. The practical case is a bird with congealed blood on its head, or a rooster pecked by others until it bled. And a sharp detail: it is treif even if the wound has since healed over on the outside — which is why it must be checked promptly, before healing makes the hole undetectable.

For what precedes all of this, see what shechita involves and what invalidates shechita. Anything you actually find is a question for your rav.