Surrogacy scams are, while rare, unfortunately not all that uncommon. Typically, a female fraudster promises to carry a couples’ fetus to term, but along the way pads the bill well beyond what one would have reasonably expected. But when Jamie Townsend and Lydia Fairchild separated in 2002, authorities believed they had an arguable more insidious scheme in front of them — a surrogate who kept the children for herself, in order to collect welfare payments.

They were wrong. Fairchild had done nothing of the sort. But the truth was even stranger.

After the split, Fairchild — pregnant at the time with Townsend’s child — requested government assistance in her home state of Washington. She claimed that she had two children, both from Townsend. Washington, to combat welfare fraud, required DNA tests from new applicants and their families — the state wanted to make sure that the children are actually that of the claimants — which Fairchild gladly agreed to provide.

But the DNA didn’t match. According to the tests, the children Fairchild had been claiming were not her own.

Fairchild protested, offering pictures of her two previous pregnancies, photos from the delivery room, and even the testimony of the delivering obstetrician. But those, the government argued, could be faked, while DNA couldn’t. Fairchild, they concluded, was lying, which meant that the two children in her custody weren’t hers — and her pregnancy, who knows? Thoughts of surrogacy fraud entered the picture. To prove it, the court ordered that an observer be present when Fairchild give birth and that a DNA test occur in the first moment of the new baby’s life.

Again, the DNA failed to match. Fairchild, it seemed, was somehow stealing eggs and ultimately, children, all as part of some complicated con game. She was almost certain to spend the next untold years living in a prison cell — until her lawyers discovered the story of a Boston-area woman named Karen Keegan.

According to ABC News, Keegan needed a kidney transplant, and her family members — including her children — underwent tests to see if any of them could be a viable donor. Instead, doctors discovered that Keegan had different DNA than her children, a familiar story to Fairchild’s attorneys. Keegan’s doctors concluded that she had something called chimerism (from “chimera,” a part-lion, part-snake, part-goat from Greek mythology, represented above), a rarity to say the least. ABC News explained: “In human biology, a chimera is an organism with at least two genetically distinct types of cells — or, in other words, someone meant to be a twin. But while in the mother’s womb, two fertilized eggs fuse, becoming one fetus that carries two distinct genetic codes — two separate strands of DNA.” In Keegan’s case, a sample from a thyroid nodule contained the same DNA as her children, even though most of the rest of her did not.

There are only a few dozen documented cases of chimerism in humans worldwide, and it turns out that Fairchild was one of them. Doctors administered a pap test, discovering DNA that matched her children. She had two different sets of DNA, and was innocent of all charges levied against her.

Bonus fact : If you want to tell two identical twins apart, a DNA test won’t help, because they have the same DNA. What will help? Their belly buttons. Belly buttons are scars, as Wikipedia notes, and are not determined by genetics. (Fingerprints also work here — identical twins do not have identical fingerprints — but that’s not as much fun.)

From the Archives: Super Twins: Crazy biological happenings like the above. Contains the term “heteropaternal superfecundation,” and yes, defines it, too!

Related: “Twins,” starring Danny DeVito and Arnold Schwarzenegger.