Livestock are being found with eyes, tongues and other body parts cut neatly out. There are no tracks or bloodstains. It's been happening, off and on, for decades. Manuel A. Sanchez has ruled out every logical explanation for the fate that has befallen the calves on his ranch in southern Colorado. Over the past month, he's found four calves dead in a way that he cannot reconcile with anything in his 50 years of raising cattle: eyes and ears missing, tongues and genitals excised in what appeared to be a series of fine cuts. Mountain lions, bears or coyotes would leave messier marks, he said. And Sanchez found no tire tracks or footprints that would suggest a human invader -- nor even bloodstains he'd expect to find around the carcasses if someone had butchered them. It's not the first time. In the 1970s, ranchers in eastern and southern Colorado filed more than 200 mutilation reports, according to Colorado Bureau of Investigation reports. The agency investigated, even conducting an undercover operation, but to no avail. It was such a bewilderment," recalled Tillie Bishop, a state senator at the time. Some people suspected satanic cults. Others grew convinced of an otherworldly explanation -- space aliens. In the mid-1990s, 27 cattle in northern New Mexico were mutilated in 16 months, the Associated Press reported. Again, ranchers found cattle with genitals removed, tongues cut off at the roots, and eyes and ears missing. The incisions appeared to have been cauterized, they said.