Archaeologists have long assumed that Maya tools like obsidian blades, bone needles and even stingray tails found in ritual contexts were used for bloodletting rituals. The problem is, it's hard to be sure. Researchers find obsidian blades all over the place, and many of them appear to have been used simply as kitchen knives.

Now, archaeologists are using new techniques to identify these tools—sharpening our understanding of how common bloodletting was and giving insight into the social contexts that drove the practice.

The practice of bloodletting was used to open a dialogue with gods or ancestors that could help the ancient Maya, says James Stemp, an archaeology professor at Keene State College in New Hampshire.

“The Maya kings and queens would often have to conduct blood-letting rituals in order to gain the favor of the gods and their ancestors," says Stemp, who is the author of a study recently published in the Journal of Archaeological Science: Reports. “In a world where everything is controlled by the supernatural, the Maya believed that their abilities to contact the supernatural ... was the main way in which they could kind of control what was happening to them."

But everything has a price, and the gods took their payment in blood. While sometimes this meant sacrificing others, a small personal donation would do in a pinch.

“Among the more common [body parts] would be earlobes, nostrils, lips and tongues. For the males, we know that they also bloodlet from the penis," says Stemp.* After piercing or slicing into themselves, they would let the blood—which was believed to contained life force—drip onto cotton or another material which they would then burn. “As the smoke comes through the air, the Maya gods or ancestors will appear to the Maya and give them the information they need to be successful in whatever they want," Stemp said, noting that this these gods would often appear in the form of a medium known as the "vision serpent."

Historians have gleaned some of this knowledge through depictions in Maya artwork. Stone carvings depict the heads of gods emerging directly from these "vision serpents," which were thought to be a gateway to the supernatural world, Stemp says. One famous Classic period carving from Yaxchilan, in modern day Chiapas in southern Mexico, shows Lady Xoc, a 7th century queen consort in the ancient Maya city, drawing a barbed rope through her tongue.

Diego de Landa, a bishop of Yucatan in the mid-16th century known for committing atrocities against the Maya, reported other gruesome details in his book Relation of the Things of Yucatan:

At times they sacrificed their own blood, cutting all around the ears in strips which they let remain as a sign. At other times they perforated their cheeks or the lower lip; again they made cuts in parts of the body, or pierced the tongue crossways and passed stalks through, causing extreme pain; again they cut away the superfluous part of the member, leaving the flesh in the form of [s]cars. It was this custom which led he historian of the Indies to say that they practised circumcision.”

Bloodletting practices likely continued among some Maya in traditional areas even up until the early 20th century, says Stemp. But it wasn’t an everyday affair—which poses a challenge for archaeologists looking for certain use-wear patterns on obsidian blades and other tools of the trade, to determine whether they were used to let the blood flow. To do that, Stemp needed to use fresh replicas of the tools and see how they worked.

Performing the practice himself, though, didn't seem like a great idea. “The thought crossed my mind,” he says, “but I’m afraid something would go horribly wrong.”

So he and other researchers, including Jaime Awe from Northern Arizona University, wisely decided to try the replicas on pigskin instead. After performing the bloodletting techniques using these tools, they found certain patterns they could identify using powerful microscopes. They then compared these patterns to those left on actual obsidian blades, and found some matches.

Once they knew what they were looking for, they examined blades collected in western Belize that date mostly to the late Classic period, between 600 and 900 A.D. Since the blades were found in places with ritual significance to the Maya, such as the Handprint Cave—caves are thought to be portals to the underworld—or around graves, archaeologists were already fairly sure they weren't used for everyday kitchen cutting. But the light wear on the blades used for human blood letting separates the tools from other ritualistic uses such as animal sacrifice, which often involved cutting through harder tissue like bone.

While replicating and testing the blades may seem like the obvious route, not many researchers have taken this approach because it’s time consuming and requires specialized equipment, says Antonio Curet, associate curator of Caribbean, Central American and Mexican archaeology at Smithsonian's National Museum of the American Indian. "It's not the smoking gun," he says, but it can provide another line of evidence that helps archaeologists get closer to the truth.

Stemp hopes to refine the technique enough so that large numbers of blades and other bloodletting tools can be analyzed from different parts of the Maya world. If enough of these tools are found across different regions or time periods, archaeologists may be able to discover whether the practice picked up or died down in periods of social turbulence. Curet agrees. "You could identify changes with it," he says. "It could become one of the strong lines of evidence."

For instance, there is some suspicion that the practice picked up near the end of the 10th century, just before the mysterious decline of much of the Maya world. “Bloodletting ramps up a lot at the very end of that classic period, right around the time that the Maya civilization collapses," Stemp says. “Maybe when they see their world crumbling down around them, they are frantically trying to communicate with the gods around them.”

*Editor's Note, September 1, 2016: An earlier version misstated that Maya commonly let blood from teeth; actually, they let blood from their tongues.