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The "secrets of sex" from 1720 have recently been unearthed, and have given us some interesting insights into the bizarre bedroom beliefs our ancestors had. 

The contents of the book are so raunchy that it was banned for almost 250 years. The book, titled Aristotle's Masterpiece, has now gone on sale after being unearthed recently.

The sex manual, which was dubbed the dirtiest book of the time when it was first published, talked about "women's unnatural lying with beasts" and also included multiple woodcut illustrations of the creatures born from such unions, Daily Mirror reported.

Jim Spencer, a books and manuscripts valuer with Hanson's Auctioneers, said: "For example, it includes woodcut illustrations of 'monsters' that 'are begot by Women's unnatural lying with Beasts' — an example being a woman 'generating with a dog'."

Spencer added: "There are several illustrations of beast-like creatures including a man sporting a bushy dog's tail and a monster being born in Ravenna, Italy, in 1512."

If you think that's weird, the authors also suggest in the book that imagination during sex influences a child's look.

Spencer added: "The book even claims parents' imaginations produce a child's features and includes an illustration of a 'maid all hairy and an infant that was born black by the imagination of the parents'."

The book encourages women to 'look earnestly' at their husbands so that their children resemble them. It also talks about the diet and astrology that will help couples determine whether they will have a boy or a girl. And, of course, marriage is considered important for all couples.

It states: "Without a doubt, the uniting of hearts in holy wedlock is of all conditions the happiest, for then a man has a second self to whom he can unravel his thoughts as well as a sweet companion in his labor."

It also offers "A Word of Advice to both Sexes in the Act of Copulation": "I do advise before they begin their conjugal embraces to invigorate their mutual desires and make their flames burn with a fiercer ardor by those endearing ways that love can better teach than I can write."

The book also recommends a list of foods to help in men's sexual function. These include eggs,  blackbirds, sparrows, gnat snappers, partridges, thrushes, parsnips, young pigeons, ginger, and turnips.

The manual also suggests how to give birth to a boy or girl: A woman should lie on her right after sex to have a boy or on the left for a girl.

The rare book will be sold at Hansons Auctioneers Library Auction on March 27.