If you’re a bovine veterinarian, one of the tools in your arsenal might be the cow magnet.
Cows don’t have four stomachs. That’s a myth. But their stomachs do have four chambers, each with a specific specialty. The second of those chambers is the reticulum. If you’ve ever eaten tripe, with its distinctive honeycomb look, you’re eating the reticulum.
A cow’s reticulum is a fluid-filled sorting device. Particles of food enter the reticulum from the rumen, and then the reticulum squeezes those particles either back into the rumen (if they’re too big) or on into the omasum (if they’re ready for the next stage in digestion).
This process is extremely handy if you’re digesting plant matter: those big chunks of grass return to the rumen and are regurgitated as cud. The cow chews them into smaller bits and they get another go at the reticulum sorting. But there’s a catch. Sometimes things get stuck in the reticulum.
Cows aren’t particularly discriminating eaters. If they bite off more than they can chew, they’ll just store it to chew later. But this means that cows end up eating all kinds of junk, like bits of fence wire or nails. And those hard metal objects end up wedged in that honeycomb pattern of the reticulum.
The technical term for this problem is (amusingly) “hardware disease.” The reticulum’s contractions can shove those pointy metal things right through the cow’s stomach wall. And, in an act of shockingly poor creature design, the reticulum is right next to the heart. So those pointy metal things may end up giving the cow a literal heartache.
The solution is simple: magnets.
Vets will insert a strong magnet into the cow’s reticulum. It works a little like Tony Stark’s chest-mounted arc reactor in the first Iron Man film. The magnet attracts all of the nails, wires, and other metal objects lingering in the reticulum and keeps them from causing further damage. Some cattle breeders will feed magnets to cows preemptively, to protect against future pointy metal things.
But what happens to that ball of magnet and metal? Well, it just stays in the reticulum permanently. Not so fun for the cow, but a lot better than a nail to the heart.
[Thanks to Basic Instructions.]
The Generalist Academy 
Delightful and disgusting simultaneously, thank you