Education can be big fun sometimes, especially when it comes to unusual facts about sex. Here are a few that we're pretty sure you'll enjoy to learn about. 

1. Semen can be used as um, invisible ink

During World War I, members of the British Secret Intelligence Service (MI6) discovered that you could use semen as invisible ink. Apparently, it didn’t react with iodine vapor (the main method used to detect invisible ink) and, as a bonus, it was also readily available. They stopped using it once they realized that it began to smell if it wasn’t, uh, fresh. Disturbing, but true!

2. We spend copious amounts of money on sex on the internet

Sex is big, big business. According to a 2005 study published in Sexual Addiction & Compulsivity, more than half of all spending on the internet is estimated to be related to sex. That’s a LOT of porn and sex toys. 

3. Sperm contains calories

While spitting or swallowing semen is always a matter of personal preference, if you’re on a diet you may want to reconsider swallowing. Why? There are 5 calories in a teaspoon of semen. And it all adds up, you know.

4. There's a reason why it's hard to wee after sex

After you orgasm, your body releases an anti-diuretic hormone, which explains why you may have trouble urinating directly after sex. Stick with it though – going to the toilet after sex helps to prevent urinary tract infections.

5. You can increase your bust size by having sex

Ladies, forget push-up bras – just get frisky instead. A woman’s breasts can swell up to 25 per cent when she’s aroused. And about one per cent of women are able to orgasm through the stimulation of their breasts and nipples alone. 

Source: Body and Soul Australia