Why do pimples and acne form?
	Acne is an infection of the skin , caused by changes in the sebaceous glands .
Why do birds sing?
	All birds make sounds to communicate .
Why do birds nest in trees?
	A bird nest is a place where a bird lays its eggs .
Why do cats get hairballs?
	After licking their fur , cats sometimes get hairballs .
Why are leaves green?
	Leaves are normally green in color , which comes from chlorophyll found in plastids in the chlorenchyma cells .
Why do mosquito bites itch?
	The feeling of itchiness can be caused by a movement of hair or the release of a chemical ( histamine ) from cells under the skin .
Why do moths fly to the light?
	Most scientists think that this is because moths use the light of the moon to help them fly in a straight line .
Why do neutral atoms have the same number of protons as electrons?
	Most atoms have a neutral charge ; because the number of protons ( positive ) and electrons ( negative ) are the same , the charges balance out to zero .
Why do ostriches bury their heads in the sand?
	It is sometimes said that ostriches will hide their heads in the ground when they are scared , but this is not true .
Why do people do drugs when they know it's bad for them?
	Other drugs are taken for fun , because of the effect they have .
	People might also use drugs recreationally ( to have fun ) .
	Some people also use drugs because they are addicted .
Why do people yawn?
	Observing another person 's yawning face ( especially his/her eyes ) , even reading , or thinking about yawning , or looking at a yawning picture can cause a person to yawn .
	The immediate cause for contagious yawning may be the mirror neurons in the frontal cortex of certain vertebrates , which , upon being exposed to a stimulus , activates the same regions in the brain .
	Often , if one person yawns , this may cause another person to `` empathetically '' yawn .
	In 1508 , Erasmus wrote , `` One man 's yawning makes another yawn. , '' and the French proverbialized the idea to `` Un bon bailleur en fait baillier deux . ''
Why do we laugh?
	Laughter can be observed in human babies from around three or four months and is usually an expression of surprise .
	Some comedies make the audience laugh by showing strange or unusual images or situations that do not make sense .
	A laugh is a way of showing happiness .
	When people are ashamed or embarrassed , sometimes they react by laughing .
Why do we sweat?
	Sweat can be made in response to nerve stimulation , hot air temperature , and/or exercise .
	The body makes sweat to cool itself down .
	Perspiration , or sweat , is your body 's way of cooling itself , whether that extra heat comes from hardworking muscles or from overstimulated nerves .
	Sweating is your body 's major way of getting rid of excess body heat , which is produced by metabolism or working muscles .
	Sweating responds to emotional state .
Why do we wear underwear?
	Underwear can be used to protect the wearer 's modesty , as well as to make them look sexy .
	Underwear can be used to keep the wearer modest - for instance , some women wear camisoles and slips ( petticoats ) under clothes that are see-through .
	In countries where the weather is cold , underwear is one more layer of clothing that helps the wearer to keep warm .
	They keep outer clothes from being made dirty by sweat .
	Women 's brassieres ( bras ) provide support for their breasts , and men 's briefs do the same thing for the male sex organs .
	They also shape the body and provide support for parts of it , and in cold weather help the wearer to keep warm .
Why does sweat cool the body?
	The sweat takes the heat from the body when it evaporates ( turns to gas ) .
	When sweat evaporates from the surface of your skin , it removes excess heat and cools you .
Why does sweat smell bad?
	Sweat itself has no odor , but when bacteria on the skin and hair metabolize the proteins and fatty acids , they produce an unpleasant odor .
Why does ice float?
	Unlike other liquids , water expands as it freezes to become ice ; so ice floats on water because ice has less density than water .
Why does it rain?
	The air cools and the water vapour condenses , forming rain drops .
	Relief or orographic rain is formed when air is forced to cool when it rises over relief features in the landscape such as hills or mountains .
	As it rises it cools , condenses and forms rain .
	When the temperature of the rising air falls to the dew point , water vapor shrinks into thick clouds and forms convection rain .
	When the clouds can no longer hold the water droplets , relief rain begins to fall on the windward slope of the mountain .
Why do we scratch when we itch?
	Pain creates a reflex withdrawal while itch leads to a scratch reflex .
	Sometimes scratching relieves isolated itches , hence the existence of devices such as the back scratcher .
	Itchiness is regarded as protective , as it helps creatures remove parasites that land on their skin .
