To signal her readiness to mate, a female rat will arch her back, raise her tail, and stand firm so the male can mount. (We hope to god you didn’t already know that.) Using this rat-sex principle, researchers at Rockefeller University isolated the chemical and physical mechanism responsible for the female’s behavior and, long story short, showed a strong connection between sexual arousal and the flow of potassium ions in the brain. Even better news: the average price of bananas (which are loaded with potassium) is about $.44 / lb! Talk about a cheap date.