10 Weird Things Humans Do Every Day, and Why

How odd that sadness causes water to spill from our eyes! Among all animals, we alone cry tears of emotion.

Not only do they serve the purpose of communicating feelings of distress, scientists believe tears also carry certain undesirable hormones and other proteins that are produced during periods of stress out of the body, which may explain the cathartic effect of "a good cry."

It's weird, when you think about it, that swapping spit seems romantic. Turns out it's a biological instinct.

Kissing allows people to use smell and taste to assess each other as potential mates. People's breath and saliva carry chemical signals as to whether they are healthy or sick, and in the case of females, whether they're ovulating — all important messages for potential partners in reproduction.

Furthermore, the skin around peoples' noses and mouths is coated with oils that contain pheromones, chemicals that broadcast information about a person's biological makeup. When people pick up each other's pheromones during a sloppy kiss, they'll subconsciously become either more or less sexually attracted to each other depending on what they detect.

Alongside the chemosensory cues exchanged during kisses, psychologists also believe the actual physical act of kissing helps couples bond. This theory is supported by the fact that oxytocin — a hormone that increases most peoples' feelings of sociality, love and trust — floods brains when mouths kiss.