In 2016, during an examination of Anne Frank's original red-checked diary, researchers at the Anne Frank House came across two pages that had been completely covered with adhesive brown paper.

While these pages had been encountered before, Frank's diary is reportedly only examined by its safe keepers once every decade or so. The difference, this time, was that advances in photo-imaging software made it possible to decipher the words beneath the brown paper without endangering the fragile document.

In May 2018, the Anne Frank House revealed the words of these hidden pages for the first time since its author scribbled them out, more than two months into a two-year hideaway from the Nazis in the secret annex behind her father's business in Amsterdam.

The pages contained 'dirty' jokes and 'sexual matters'

"I'll use this spoiled page to write down 'dirty' jokes," Frank began her entry dated September 28, 1942.

She proceeded to do just that: "Do you know why the German girls of the armed forces are in the Netherlands?" she wrote. "As a mattress for the soldiers."

For an encore: "A man comes home at night and notices that another man shared the bed with his wife that evening. He searches the whole house, and finally also looks in the bedroom closet. There is a totally naked man, and when that one man asked what the other was doing there, the man in the closet answered: 'You can believe it or not but I am waiting for the tram.'"

The entry also delved into matters of a changing body and sexual curiosity. At one point, Frank described how a girl her age is due for her first period, calling it "a sign that she is ripe to have relations with a man but one doesn't do that of course before one is married."

As for these relations, Frank had clearly given the topic some thought: "I sometimes imagine that someone might come to me and ask me to inform him about sexual matters," she mused, wondering, "How would I go about it?" She proceeded to depict what she imagined were the "rhythmical movements" involved, as well as the "internal medicament" used to prevent pregnancy.

Frank also revealed that she was well aware of grown-up topics like prostitution: "All men, if they are normal, go with women, women like that accost them on the street and then they go together," she wrote. "In Paris they have big houses for that. Papa has been there."

Altogether, according to the Anne Frank House, the two pages were filled with "five crossed-out phrases, four dirty jokes and 33 lines about sex education and prostitution."

The diary of Anne Frank
The diary of Anne Frank; Photo: Fine Art Images/Heritage Images/Getty Images

Each edition of the book revealed more explicit entries

It's unclear why Frank covered up these particular pages. Although the original 1947 publication of Het Achterhuis, culled from her diaries and her father's edits, became famous for its innocent addresses to "Kitty" and other imaginary figures, more explicit entries had surfaced with the release of expanded editions in 1986 and 1991.

These included stark explorations of her body: "Until I was 11 or 12, I didn't realize there was a second set of labia on the inside [of her vagina], though you couldn't see them," she wrote at one point. "What's even funnier is that I thought urine came out of the clitoris."

Frank also had harsh observations about her family, the hideout's co-inhabitants and the helpers who brought them supplies, which certainly would have sparked hurt feelings had they been discovered at the time. These included unsparing comments about her mother, "the old nanny goat," and her disgust at her father's "fondness for talking about farting and going to the lavatory."

Frank seemingly intended to preserve just about everything she wrote, even before she focused on a possible future publication upon hearing Dutch minister Gerrit Bolkestein's March 1944 radio announcement about the importance of documenting the atrocities of the Nazis.

Frank used her diary to express thoughts she was 'not comfortable with'

Regardless of Frank's reasons for covering the two pages, the revelation of its contents marked another step in the ongoing exploration and analysis of her prolific output while isolated from the outside world.

According to researcher Peter de Bruijn of the Huygens Institute for the History of the Netherlands, the newly discovered passages are important because they reveal Frank's development of her craft. "She starts with an imaginary person whom she is telling about sex, so she creates a kind of literary environment to write about a subject she's maybe not comfortable with," he explained.

Observed Anne Frank House Executive Director Ronald Leopold, more succinctly, "They bring us even closer to the girl and the writer Anne Frank."

Remarkably, it seemed there was more to be gleaned from documents that had been closely guarded and examined for decades, and potentially still more to learn about their author, more than 70 years after her young life was cut short in a concentration camp.