How the prisoner actually dies still isn’t totally clear, according to Denno’s research, but electric-chair deaths are some sort of combination of asphyxiation and cardiac arrest, and the nervous system is usually paralyzed. The body tenses up—sometimes violently—and inmates often defecate. Smoke and steam rise out of the body probably because the inmate’s blood is boiling. The inmate’s temperature become so hot, flesh falls off if someone touches the body, and the inmate usually receives third and fourth-degree burns under the electrode cap. I asked Denno if the eyeballs pop out. “Sometimes the eyeballs can pop out,” she said. The body can also bleed because of the pressure of the expanding tissue. Denno said, “It’s horrible, but it’s really like the body is cooking.”

And that’s what happens when the execution goes well. If the process is botched, Denno said, the results can be even more gruesome. In two Florida executions during the 1990s, for example, flames burst out of the inmates’ hoods, because prison officials used the wrong sponges. In another particularly grisly case, Florida death row inmate Allen Davis’s 1999 electric chair execution went horribly awry, leaving Davis with burns on his face and covered in blood from a nosebleed. Evidence showed Davis had been partially asphyxiated by a mouth strap that had tied him to the chair, according to Denno’s research.

Perhaps the worst-case scenario, though, is when the inmates don’t actually die after the first few minutes in the electric chair. “When there have been botched electrocutions, it’s often because there is a problem with the electric current,” Denno said. “When that happens, the inmate doesn’t seem to be dead during the first jolt—it can be enough electricity to be extremely painful, but not actually kill the person. Someone could be burning to death and dying, but be consciously aware and not able to cry out.”