Joe here. How are you feeling today? How are these definitely not generic（[生物]属的） stock（树干） photo people feeling? Are they neutral（中立的）, ashamed（惭愧(的)）, stoically handsome? Sometimes it can be a little hard to tell, but if we add a few tears（ 眼泪） to these facial expressions, voila! These people look super（特级的） sad.

  When we see faces get all contorted and messed up and liquid leaking（漏） out of eyeballs（眼球）, that sends a clear unambiguous emotional（感情的） message, because we are the only animal that cries. Why? On a blueprint（ 蓝图）, title. It's okay to be smart. Pain, sorrow, dangerous foreign objects. All of these things can make（使） people cry.

  This reaction makes sense when, say, dust gets in your eye, which always seems to happen to me when I watch the beginning of Up. It appears in a thought bubble. You make tears to flesh your eye clean, but what's the point of making tears when we're sad? Why did humans evolve（发展） emotional（感情的） crying? We make a few kinds of tears. Tears of sadness are called emotional or psychic tears.

  They differ（使…相异） from reflex tears（ 眼泪）, which we make to flesh our eyes in response to irritants. We even make a third type of tear, basal tears, a liquid force field we're constantly（不断地） producing to protect and lubricate（润滑） our eyes. Each tear type has a different recipe. All three contain salt, proteins（蛋白质）, and antibacterial enzymes（[生化]酶）, but emotional（感情的） tears（ 眼泪） have higher amounts of protein（蛋白质）, including stress hormones（荷尔蒙） and natural painkillers that we don't yet know the purpose of.