A phenomenon often associated in the pop media with UFOs, satanic cults or the paranormal, but in the real world more likely connected with insurance. The typical scenario is like this: A farmer living in the middle of nowhere reports that he saw a flashing light (or other such vague UFO-ey evidence), and when he went outside to investigate, he found his cattle dead, with parts of their bodies cut off, but no blood on the ground!
The sci.skeptic FAQ has this to say: