British scouts launched sex education classes in a bid to help tackle the country's high rates of sexually transmitted diseases.
The Scout Association is adding learning about the birds and the bees to its more traditional activities such as camping, canoeing and climbing.
The programme, for scouts aged 14-18, is designed to encourage young people to learn about relationships and sexual health "with their peers and trusted adults," said the group.
The "fluid exchange game" uses plastic cups and food colouring to demonstrate how quickly fluid and infection can spread.
Britain is the sick man of Europe when it comes to sexual health, with the highest rates of sexually transmitted infections and teenage pregnancies, according to official figures.
"We want to help young people become confident, clued up and aware," said Bear Grylls, chief scout and presenter of TV adventure shows.
"We only get one body, so respect it and people will respect you."
The association said that scout groups will be given material for the course but insisted that individual scout leaders can choose whether or not to run the programme.