We laugh due to an area of the brain in the subcortex which is an ancient part of the brain. This area also controls reflexes and breathing. It is hard to hold in a laugh or to laugh on demand. All humans laugh and make similar noises when they do so by using the parts of the body that produce talking and breathing. We spend about 1/3 of our lives asleep. It is a required activity regulated by a 24 hour rhythm called circadian rhythm. In the evening, a pressure or drive to sleep reaches its peak. Next, adenosine levels which have been building reach a peak and this causes you to feel sleepy. When it gets dark, a hormone melatonin signals your body its time to sleep and you get drowsy. Crying is when tears are shed due to an emotional state. There is a connection between the lacrimal gland or tear duct and parts of the brain where emotions lie. Tears produced when crying contain the hormones prolactin, adrenocorticotropic hormone, potassium and manganese. These differ chemically from other types of tears. Tears are a way to nonverbally communicate being in pain, to release stress, to get others to be sympathetic, to release toxins, among other reasons.