It would be easy to think that a duck’s feathers would soon become waterlogged so that it would sink,
but in fact, ducks, geese and swans, as well as seabirds, have waterproof feathers, which enable them
to swim and dive beneath the surface of the water. Ducks create this waterproofing using the oil from
the preen gland, near the base of the tail, which they spread through their feathers and the underlying
dense layer of down with their bills. A layer of fat under their breast skin also helps to keep them
buoyant. Different ducks feed in different ways, some dive, some upend and feed from the bottom of
the lake or river while others ‘dabbles’, stirring up the water with their feet to find food.

Dinosaurs lived for an enormously long time-some 150 million years – before they died out about
64 million years ago. All the dinosaurs disappeared at about the same time. However, whether
this happened over a few days, a few years, one or two centuries, or even a few thousand years is
impossible to say. Many people believe that the dinosaurs became extinct as a result of climate change
after a huge meteor or a small asteroid struck the Earth. The extinction of the dinosaurs was not an
isolated event. At the same time most marine reptiles and pterosaurs also died out.

Several families of birds can be trained to ‘talk’, but in reality they are simply mimicking noises without
really understanding what they are saying, although they can be taught to associate a given word or
phrase with a given action, for example saying ‘give us a peanut’ to get a reward. The best talkers are
parrots and mynas, and members of the crow family such as crows, jackdaws and ravens can also learn a
few simple words. They can do this because the are highly intelligent birds and they are excellent mimics
in the wild. Other bird mimics that do not pick up speech are starlings and some of the bowerbirds in
Australia, including on individual that had learned to copy the noise of the logging machines that were
destroying his habitat.

Construction of the famous white marble bell tower (campanile) of Pisa’s cathedral began in 1173 but by
the time three stories were built, it had already begun to lean. Over the centuries, many methods have
been tried to prevent the lean getting worse but as most people did not understand what was causing
the lean, they made it worse. The soil under the tower is very soft and waterlogged in parts, which is the
most plausible explanation for the lean. In 1990, the tower was closed to the public because cracks in
the walls were worsening and it was feared that it might topple over. Since then, straps and cables have
been used to hold it in place, 800 tonnes of lead weights have been added to the high side of the base
and 38 cubic metres of soil removed from that area, which has stabilized the tower, and even reduced
the lean slightly.

The simplest way to describe an optical illusion is that it is a ‘trick’ that our eyes play on us. We seem to
see something that isn’t really so. Or we may be able to see the same object in two completely different
ways. If our eyes are working properly, and they are instructions for seeing exactly what is before
us, how can they play such tricks on us? This is because vision is not a physical process. It is not like
photography, for instance, which work mechanically. Vision is really a psychological experience, because
it is not the eyes that see, but our brain.

We all dream at night, although we may not remember our dreams in the morning. Although scientists
do not precisely understand how we dream, they have discovered that it is important for us to do so
and people who are prevented from dreaming soon begin to feel unhappy. We are deeply asleep when
we dream, but our brains are active. Scientists think that our brains may be working though the events
of the day, storing memories, making sense of our emotions and preparing us for the next day, Dreams
are often unrealistic or even weird, putting us in odd situations. Bad dreams, called nightmares, may be
particularly vivid and we may be more likely to remember flashes from them because the emotions the
created were so strong that they made us wake up.

If this question had a simple answer, such as a formula that could be learned, you can be sure that every
comedian would know it! But laughter is a complicated things, and the best explanations of it are still
only theories. We know, of course, that laughter is an expression of many feelings and that laughter is
only found among human beings. It is difficult to decide what really makes people laugh, because each
person will find a different thing funny. It is all down to being individuals. From the physical point of
view, laughter is very good for us. It is good for our lungs, and it is an outlet for some extra energy. So
although no one really knows what makes people laugh, or what the purpose of laughter is, it is a very
good medicine and certainly makes us feel better.

Early man had to rely on his own muscle-power to carry objects, but over thousands of years tamed
animals, such as horses, oxen and donkeys, elephants and camels. In order to be able to transport more
goods than an animal could carry on its back, sledges and hurdles that could be pulled behind the animal
were eventually invented, as well as such instruments as ploughs to make agriculture easier. Where
sledges were not suitable, such as on rough ground or sand, the could roll heavy objects along on top
of logs, continually taken from behind the object as it passed and placed in front of it. It is thought that
stones for both the pyramids and Stonehenge may have been moved using this technique. Eventually,
someone realized that attaching the logs, or sections of log, to the object would be more efficient and

There are more than 150 species of octopus, ranging from the very small to the giant octopus, which
may reach 33ft (10m) in length. Most of them eat crabs, fish, crustaceans and smaller mollusks, which
they catch and tear apart with their suckered tentacles. An octopus’ mouth is shaped like a parrot’s
beak, with two very strong jaws. In addition the octopus can inject venom or poison with its bite,
which enables it to disable prey that might fight back, such as crabs, more quickly. Octopses are very
intelligent, curious animals, with a highly developed nervous system and extremely good eyesight.
They propel themselves through the ocean by squirting water from the edge of their mantle. They are opportunistic feeders , which means that they will tackle almost anything when they are hungry!

Pearls, whether natural or cultured, are made in the bodies of some species of oysters and are
composed of the same material as the iridescent mother of pearl that lines oysters’ shells, which is a
form of calcium carbonate. If something, such as a grain of sand, gets into an oyster’s shell, it will not be
able to expel it and instead coats it with layers of mother of pearl, creating a spherical pearl. Because
natural pearls are rare, people make cultured ones by inserting a grain of sand into oysters in order to
force them to create pearls, which are harvested after two or three years. These are usually lower in
quality than natural pearls and often not perfectly spherical. Because of this, and because they are less
rare than natural pearls, cultured ones are less expensive to buy.