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Why are your lips red?

First of all, did you know that the outline or the border of your lips (called the vermillion border) is a special feature of humans only? This transition line from your skin to the pinkish-red part of your lips is found only in humans—no one knows why. The lips appear red because of the underlying blood vessels. Arteries and veins are connected through a series of tiny interlocking loops of blood vessels call capillaries. These red-colored blood-filled capillaries are close to the thin skin on your lips, so your lips appear red.

Why doesn't it hurt when you get a haircut?

Your hair is made up of two main parts—the hair follicle and the hair shaft. The follicle is the root that sits inside the scalp and contains the part of the hair that is alive and can feel pain. The hair shaft is the part of your hair that is outside the scalp that you can see. It is made up of protein called keratin—but this protein does not contain living cells. Therefore, when you cut the keratin protein it doesn't hurt. But you do feel pain if your hair is yanked out of the scalp, because the hair is being pulled out of its root, the living part of the hair.

Why do I laugh when I think something's funny?

Humans are not the only animals who have the ability to laugh. Smiling and laughing have been observed in non-human primate species during social play. This type of behavioral response serves as a signal to the group by spreading positive emotions, decreasing stress, and contributing to the cohesiveness of the group.

Humor-evoked laughter in humans can be divided into three stages. When listening to a joke, the first part of the humor is the punch line, an incongruous ending. Second, your mind begins to problem-solve in order to interpret this incongruity or surprise. Finally, the brain is able to appreciate these steps, which together form humor and evoke a response of laughter.

The neurotransmitter dopamine (a brain chemical) is responsible for allowing the brain to progress through the stages of humor. Dopamine allows us to feel good when we laugh. Some studies have demonstrated an improvement in health for chronically ill patients when they are exposed to funny stimuli. Thus the old adage "Laughter is the best medicine" probably has a note of truth in it.

Why, when I'm asleep at night, do I sometimes startle myself awake?

As you pass through light and deep sleep cycles during the night, your arms and legs may occasionally twitch or jerk. Sometimes the movement is enough to wake you up briefly. If you have clusters of these repeated leg jerks—at least five jerks in an hour—you may have periodic limb movement disorder (PLMD), which is characterized by leg jerks every twenty to forty seconds, each of which causes a brief awakening.

Restless leg syndrome (RLS) is another type of motor syndrome that can cause sleep problems. RLS is characterized by a creepy-crawly or pins-and-needles sensation of the lower legs, which is only relieved by moving them. Both PLMD and RLS can cause difficulty falling asleep and staying awake, which can lead to daytime sleepiness. In moderate to severe cases, prescription medication may be helpful.