1. When you kiss someone for the first time, you get a spike in the neurotransmitter dopamine, making you crave more.
2. Dopamine can also make you lose your appetite and make it hard for you to sleep.
3. Two thirds of people tilt their head to the right when they kiss.
4. Kissing helps us work out if someone is a good match.
5. When you kiss someone your heart beats faster and more oxygen reaches your brain.
6. And it makes your pupils dilate.
7. Endorphins released during kissing bring on waves of euphoria.
8. The muscle you use to pucker your lips is called the "orbicularis oris".
And the shape you make with your mouth mirrors that of a breastfeeding baby, hinting at one possible way that kissing evolved.