Some religious people had too much time on their hands

I don't know, but I think some people in India and Tibet with religious interests really had too much time on their hands.   From an article with the somewhat worrying title:  Tapping the Body's Nectar: Gastronomy and Incorporation in Tibetan Literature, I extract the following:

This essay will present a set of thirteenth-century Tibetan texts that pre-
scribe the consumption of human by-products—such as flesh, excrement,
or urine—and consider several discursive contexts in which these pre-
scriptions may be understood.....

 A gastronomic discourse of consuming human flesh and other body
products, prepared following recipes targeted at achieving siddhi and other
supernormal aims, is central to the Tibetan corpus of Nyingma tantras,
many of which are said to be based on indigenous Tibetan writings and
on transmissions that occurred during the first diffusion of Buddhism into
Tibet, during the eighth to the ninth centuries....

The Nectar Tantras collection is attributed to Vimalamitra, an Indian
who is said to have spent many years in Tibet around the turn of the
eighth to the ninth centuries and who is considered a central figure in the
transmission and dissemination of Mahayoga and early Great Perfection
(Rdzogs chen) teachings in Tibet. ...

Ok, now for some explicit instructions:

 The Eight Chapters on Nectar’s central practice involves the creation
of nectar by consecrating a brew of fluids said to emerge from sexual union
and various other ingredients. The sixth of the eight chapters contains ex-
plicit instructions on how to make nectar (bdud rtsi sbyor ba). Selecting
and purifying a suitable place, the text says, the practitioner should make
a mandala; it should be covered with excrement and urine, with five hu-
man skulls placed at the cardinal points and in the center and lit with a
lamp fueled by human fat. The practitioner should obtain the skull of a
Brahmin and place it at the mandala’s center, filled with five “fragrant
nectars” (that is, the five human by-products or products designated as
their substitutes). To that mixture a number of fruit, plant, and mineral
ingredients are to be added, as well as the five meats and the five sub-
stances that are extruded by the sense organs (the eyes, nose, ears, tongue,
and heart). More ingredients are added to the concoction: grapes, wood-
apple, mango, jackfruit, cinnamon, cardamom, nutmeg, cloves, and so
forth, plus the powder of ground-up gold, silver, copper, iron, and tur-
quoise. As the practitioner stirs this brew, he (the text presupposes a male)
chants mantras. “The excellent nectar mixed from these [ingredients] is
certain to bestow the fruits of siddhi,” the tantra asserts.

Once the practitioner has mixed his brew of nectar, he should next take
up the identity of a wrathful Heruka, he should be joined by a consort,
and the pair should engage in sexual intercourse. At this point, the text
promises, “You will achieve facility with the vastness [of Buddhahood] and
its causal conditions, and you will arrive at the samadhi of the peaceful
dharmakaya. You will become possessed of the eight worldly siddhi and
attain the empowerment of ultimate truth.”10 This ritual should be con-
ducted while the female is menstruating, and the mixture of her blood and
his semen is referred to as “the best rasayana [ra sa ya na’i gtso bo].”11
Instructions for a contemplative exercise follow. 

When the blood and  semen meet, at the five power places (gnas lnga) of the body (the crown
of the head, the tongue, the heart, the navel, and the genitals) the prac-
titioner should imagine five luminous seed syllables and five Buddhas ra-
diating light. As the light rays contract, the practitioner should grab hold
of these “five medicines” (sman lnga) for himself. The five nectars here
are each associated with a Buddha and his seed syllable: Vairocana with
excrement, Amitabha with bodhicitta, Amoghasiddhi with flesh, Ratna-
sambhava with blood, and Aksobhya with urine.12 The seed syllables then
melt into five streams of the five nectars. Repeating this visualization
many times, together with mantra recitation and hand gestures, the prac-
titioner consecrates the nectar vessel at the center of the mandala by rest-
ing his hand on its top.

I haven't heard the Dalai Lama talking up this aspect of his region's religious history.  I wonder why...

PS:  It's all a bit Temple of Doom, the imagery, I reckon.   And how come Christianity never got into sex magic rituals.  A disappointing oversight.  :)

Update:    yet more from that article, which makes going to the doctor in Tibet at the time sound like a real worry:

Gu ru chos dbang’s Accomplishing Medicine Applications (Sman bsgrub
las tshogs) offers a range of practically oriented recipes for the use of
consecrated nectar to achieve various aims. He provides a general recipe
for combining the five nectars into a concoction that may then be used as
a base ingredient for more elaborate prescriptions: “Six liters [bre] of
nectar [bdud rtsi, that is, excrement], a handful of human flesh, one
palmful of blood, half of that of white bodhicitta bezoar [go ro tsa na],
and however much urine is appropriate.”19 Recommended sources for
collecting these ingredients are provided: for example, the bodhicitta may
be the brains of a sixteen-year-old child, the blood may come from your
lama’s consort, caretaker, or female student, and the urine may be taken
from a young child born to your lama and his consort.20 ....

Following the general recipe above, Gu ru chos dbang offers a series
of prescriptions for mixtures that cure illness or enhance personal health
and power. Thus, if you mix the juice-like nectar with more than thirty
additional ingredients, including turmeric, a tooth tip, bitumen, white
aconite (bong nga), barberry bark, camphor, a young boy’s bezoar, and
various other medicinal substances, then this compound may be used to
treat contagious diseases or poisons. Adding calcite (cong zhi), pitch (brag
zhun), saffron, bal bu leaves, the three salts, pomegranate, and the flesh
of a lammergeyer to a handful of nectar will clear up bladder disease.

What the heck is a lammergeyer?   Oh - a bearded vulture, by the looks.   And "a young boy's bezoar"?  

A bezoar (BE-zor) is a solid mass of indigestible material that accumulates in your digestive tract, sometimes causing a blockage. Bezoars usually form in the stomach, sometimes in the small intestine or, rarely, the large intestine. They can occur in children and adults.

I had not heard of that before.   I wonder how you get a small boy's one in Tibet in the 13th century.  I don't want to know.