What causes headaches? MARGHERITA Apart from homework and exams, headaches are also sometimes caused by bleeding, tumours or infection inside the skull, or by diseases involving teeth, eyes or sinuses. Flu or any sickness that causes fever can also cause headaches. Such headaches are called secondary headaches because they are caused by other problems. They are only a symptom of some other disease. Headaches can also be caused by tension or stress. Most people suffer from primary headaches, including migraine, 'tension-type headaches' and cluster headaches - the headache itself is a primary problem and not just a symptom of some other disease. The majority of headaches originate within the brain. Medical evidence suggests that migraine, 'tension-type' and cluster headaches are caused by an electrical and chemical instability of certain key brain centres that regulate blood vessels around the head and the neck, as well as the flow of pain messages into the brain. This instability, similar to that which causes seizure disorders, seems to be inherited and appears to involve chemical messengers known as neuro-transmitters. These headaches can be treated by using drugs that stabilise brain chemistry. Headaches are also a common symptom following car accidents or falls, often lasting more than two months after the injury. What are armadillos? Armadillos, anteaters and sloths make up the order of mammals called xenarthra. All 29 species live in Central and South America, except the nine-banded armadillo, which lives in North America. Armadillos are burrowing animals, anteaters are ground-and-tree dwellers, while sloths spend most of their lives hanging upside down from trees. Armadillos are distinguished by their protective body armour, formed by bands of hinged bony plates capped with horn. The head is protected by a shield consisting of several plates; only the belly remains unprotected. The 20 species of armadillo live in a range of habitats including forest, desert and savanna. Most species rest in burrows during the day, emerging at night to feed on small vertebrates, invertebrates, plants and carrion. Armadillos have large claws for finding food and digging tunnels. They dig into the ground to find food, make burrows and escape from predators, loosening the earth with their front feet, then kick the soil out backwards with their hind feet. Fairy armadillos spend most of the day underground. As they dig a burrow, they block the entrance with their armour-plated rear. Hairy armadillos have hair growing out of the bony plates on their bodies. The giant armadillo is the largest of the armadillos. Its body is one metre long and it uses its powerful claws to dig into the centre of termite mounds on the forest floor, oblivious of the bites of the angry termites. Giant armadillos are found from Venezuela to northern Argentina.