Q: What causes tooth decay?

A: Wear,tear and injury may damage teeth. But in addition to these causes, bacteria can cause tooth decay. The human mouth is contains an immense number of bacteria. This is because the mouth is warm, dark, moist and contains tiny particles of food that help nourish bacteria. Both aerobic and anaerobic thrive inside the mouth. Anaerobic bacteria, those that do not need oxygen to survive, find their way inside a tooth trough tiny cracks. Once inside, where there is no oxygen, these anaerobic bacteria start to damage the tooth.

Tooth decay can be the result of feeding a colony of germs inside the mouth with food composed of refined sugars. The sugars of candies, cakes and soft drinks are easir for bacteria to digest, compared to fruits and vegetables. A tiny bit of food remaining in the mouth after a meal is enough to nourish millions of bacteris for 24 hours or more.
The formation of plaque also contributes to tooth decay. Plaque is a sticky substance that forms a film over the surface of the teeth. If not removed regularly through flossing and brushing, plaque may develop into a rough and hard substance called tartar, or dental calculus.

Q: How do dogs sniff out drugs and explosives?

A: Police and customs throughout the world use "sniffer" dogs to detect drugs and explosives.
Breeds of dogs that are trained for "sniffing" job include labradors, collies and spaniels and other retriever dogs; most popular, however, are German shepherd dogs
Dogs have a far better sense of smell than a human do because the smell receptors at top of their noses are 100 times longer than in humans.
The training course for a sniffer dog normally lats about 12 weeks. The dog is first taught to recognize a particular drug or explosive.
Its handler(the person who trains the dog) hides a sample of the substance inside something the dog can grip in its mouth- a rolled -up newspaper or a rag- which is known as a training aid.
The dog is commanded to bring the aid back to its handler, and then recieves a reward. The reward could be a food or anything that the dog enjoys doing, like a friendly fight or game.