Ambrose Pare was a medieval doctor who served as a battlefield surgeon for kings Henry II, Francis II, Charles IX, and Henry III and made great advances in pathology and surgical techniques. (He's the one who convinced people to stop pouring boiling oil in open wounds!) In addition to his many advances, he also had a lot of ideas about how monsters and monstrosities were created. Besides “God’s will” and “evil,” here are 12 ways Pare believed that monsters like man-goats and brain scorpions were created, from his book On Monsters and Marvels.

1. Menstrual Blood

Getty Images

If your baby is born with the head of a parrot, you probably only have yourself—and your menstrual blood—to blame. Pare warned that women “sullied by menstrual blood” will conceive monsters. Also, if your kid is sick a lot, it’s probably because your baby touched your dirty period. Pare wrote, “women who will have conceived during her period will engender those inclined to leprosy, scurvy, gout, scrofula, and more…”

2. Prophetic Warnings

If you see a horse with the face of a man, put down your iPhone—God is warning you of some great misfortune. Pare wrote that God often sends monsters as a signal of his displeasure. When Pope Julius II waged war against King Louis XII, for example, God sent a winged monster with both male and female bits to end the fighting, according to Pare.

3. Too Much Sperm

Bad news, men: Pare thought that men with too much seed could produce a baby with two heads, four eyes, two chests, and four hands or horns. He used a woman who gave birth to a child with horns as an example.

4. Imaginative Faculty

Pare wrote about a woman with two heads who went begging from door to door but was cast out of the country where she lived because doctors believed that if a pregnant woman saw her, she might influence their imaginations and cause them to give birth to monsters.

5. Crossing Your Legs

Pare believed that if your womb was too narrow, you could birth a misshapen child. He also argued that women who crossed their legs or bound their stomachs too tightly could give birth to monstrous putrefied babies.

6. Eating Fruit and Grasses

Getty Images

According to Pare, women who didn't eat the right food could potentially give birth to monsters. He noted that this happened to the women of Naples frequently because they prefered to eat fruit and grasses “and other bad-tasting and unnutritious (sic) things, which generate such animals through putrefaction, than to eat good nourishing food, just in order to be sparing and elegant and thin.”

7. Sniffing Basil

Pare wrote of an Italian who died of an extreme headache. When the man’s head was opened after his death, the doctor found a scorpion inside his brain, which was attributed to the man’s habit of sniffing basil.

8. Throwing a Mouse Between Your Teats

According to Pare, "some have attributed monsters to being procreated from the corruption of foul and filthy foods that women eat, or want to eat, or that they abhor looking upon just after they conceived; or [they say] that someone may have tossed something between their teats, such as a cherry, plum, frog, mouse or other thing that can render infants monstrous.” What other things, Pare?

9. Showing a Pregnant Woman Food

Modern doctors place a lot of dietary restrictions on pregnant women—no sushi, no lunch meat, watch the mercury—but none of those restrictions could hold a candle to Pare, who wrote that women could give birth to a baby that looked like a piece of bacon if that woman was shown the food and not immediately allowed to eat it.

10. Being a Sodomist and an Atheist

Generally, medieval doctors believed that if a half-human, half-animal was born, it was wrought of some serious human and animal sin. Pare described half-men, half-swine and a dog with the head of a bird to describe such unholy couplings. He then went on to say that such sin causes so many monstrosities that he couldn't and wouldn't describe them all. “For,” he wrote, “what can sodomists and atheists expect, who … couple against God and Nature with brute animals?”

11. Constellations

Getty Images

According to Pare, a farmer who had a cow with a human head was pardoned for his alleged crime against cows because an astrologer did some calculations and discovered that the monster was born of a constellation and not sin—at least not this time.

12. The Devil (obviously)

Getty Images

If your monster hasn’t been created by an excess of basil or cinching your belt too tight around your pregnant belly, it was probably made by a demon. Pare wrote that the Devil and his demons take the form of Centaurs, snakes, and other monsters who “howl at night and make noise as if they were in chains: they move benches, tables, trestles; rock the children, play on the chessboard, turn the pages of books, count money; and one hears them walking about in the chamber; they open doors and windows and cast dishes to the ground, break pots and glasses and make other racket…”

All illustrations from On Monsters and Marvels by Ambroise Pare unless otherwise noted.