Not so much a mystery, but more of a gruesome custom of the Shuar Indians of the Amazon regions of present day Ecuador and Peru. A shrunken head is a real human head, ritually prepared for spiritual protection and intimidation.
Head-hunting occurred in many regions of the world, but the practice of head shrinking has only ever been recorded in the north-western region of the Amazon rain forest by the Shuar Indians. Among the Shuar, a shrunken head is known as a tsantsa.
The practice of making shrunken heads originally had religious significance; the heads were believed to harness the spirits of those enemies and compel them to serve the shrinker. In more recent years, collectors and tourists have traded firearms for shrunken heads increasing demand and fuelling inter-tribe warfare.
After World War II, the shrunken head of a Polish prisoner was found at the Buchenwald concentration camp, where it was displayed in the camp centre to terrify the prisoners.
The Shuar believe in the existence of three fundamental spirits; Wakani to innate to humans thus surviving their death, later turning into vapour; Arutam, literally "vision" or "power," protects humans from a violent death and assures their survival and Muisak a vengeful spirit, which surfaces when an Arutam spirit-carrying person is murdered.
To block the last spirit from using its powers, they sever their enemy's heads and shrink them. It also served as a way of warning enemies.
The whole process is governed by strict rituals and feasts which around one week. The head would be worked on every day, on the way back to the warrior's village. The final stages are performed a few hours from the village, where the final feast will be performed.
The Jivaro Indians were preoccupied with realism and the utmost care was taken in order to maintain the likeness of the slain victim's face. The facial distortion and shrinkage of the lateral sides of the forehead are artefacts of the shrinking process.
As early as the 1870's people in Colombia and Panama, unconnected to the Javaros, began to make counterfeit tsantsas encouraged by this trade. They would use corpses from morgues, or the heads of monkeys or sloths. Some even used goatskin. Today it is estimated that up to 80 percent of shrunken heads are fakes.