Menstruation, erections, wet dreams, and masturbation. Reproduction: Sex, giving birth, and contraception.

: Organizations focused on sexual health and education, such as those affiliated with family planning or youth health services, might have historical data or publications on the topic.

"I'm 46 now. In 1991, my teacher in Leuven showed us a drawing of a penis and said, 'This is normal, but you don't need to talk about it at dinner.' That was it." – Jan, Flemish.