杏吧原创

Frazzled

Question: Why do people get grumpy when they are tired? Does it require more
energy to be cheerful or something?

Answer: If you are tired, communicating with other people is an effort. Your
grumpiness discourages them from trying to be sociable. Conversely, if you are
cheerful, they are more likely to talk to you and you respond. So it can be said
that cheerfulness takes more energy.

Bobby Hersom

Thirsk, North Yorkshire

Answer: You snap when you are tired, not because being cross is less energy
demanding than being nice, but because you are afraid being nice will encourage
people to stay and chat and maybe ask you to do something.

Anne Dyer

Craven Arms, Shropshire

Both these speculative answers suggest an untested evolutionary hypothesis
for irritability and grumpiness: that they are an adaptation for communicating
an urgent need to conserve energy. There is almost certainly a research grant
somewhere in the evolutionary psychology of grumpiness鈥擡d

On the hoof

Question: Why are domesticated horses given shoes? They seem to have no
difficulty managing without them in the wild.

Answer: Nature gave the horse a hoof that is perfectly adapted to its life in
the wild. That lifestyle involves up to 18 hours a day spent grazing, with some
gentle walking from one patch of grass to the next. The occasional burst of
speed is required to outrun real and imaginary predators. The ground they
inhabit is mostly soft and there are few metalled roads.

In contrast, the work of domesticated horses involves fast work on hard
surfaces, sometimes on metalled roads. If their hooves were not shod they would
wear away quickly and the hoof wall would break and crack. This would expose the
sensitive tissue underneath and the horse would become lame.

Even when horses are shod, the shoes need replacing every four to six
weeks.

Claire Adams

Belmont, Western Australia

Answer: Domesticated horses and, indeed, domesticated humans, are shod for
protection and fashion when circumstance demands.

A horse鈥檚 hoof has an upright outer wall, made of keratin (equivalent to our
fingernail), which is hard and insensitive. The shoe is nailed to this. The
concave sole on the underside of the hoof is sensitive and not as hard as the
outer wall. To the back of the sole is the frog, a heart-shaped bulb of
insensitive gristle that acts both as a shock absorber and an aid to circulation
when it is compressed at each stride.

The hoof is wonderfully evolved to stop a horse鈥檚 leg from fraying at the
end, but is neither so solidly resistant that the horse cannot feel the ground,
nor that its legs and frame will suffer from the effects of concussion each time
a hoof hits an unyielding surface.

Without wear, the hoof wall grows downwards beyond the sole about 5
millimetres every month. The sole regenerates constantly but at the same time
flakes away. In the wild, a horse must wear away the wall at the same rate as it
grows or the relationship between wall and sole will not be maintained.

If the horse is kept on green grassland which is fairly damp and soft, the
wall soon becomes too long and must be trimmed back or it may break and split,
causing damage to the foot. If it is ridden unshod on a hard surface, the wall
soon wears right down into the sole, and the horse becomes footsore and lame. So
the hoof wall growth/wear factor would seem to indicate the terrain of the
horse鈥檚 natural habitat: arid grassland seems to fit the bill.

However, not all horses are the same. Evolution has given us the light desert
horse of North Africa and the Middle East, the heavy forest horse of Europe, the
steppe pony of Asia and the Celtic pony of Britain. Each evolved on different
terrain and has hooves to match.

Modern breeds stem from these varieties, and feet vary accordingly. Dark,
pigmented hoofs are generally harder than light ones; small ponies often have
tight, upright 鈥渄onkey鈥� feet, which suit compact ground; while big carthorses
usually have 鈥渄inner-plate鈥� feet to support their weight on soft ground. But
horses have yet to evolve a hoof suitable for constant wear on hard surfaces or
rough stony tracks. Stones may damage the frog and the sensitive sole, and can
cause pain, bruising and even puncture wounds. Shoeing affords protection but
does not completely eliminate the problem, mainly because in the wild a horse
can choose where it puts its feet yet, when controlled by a human, sometimes it
cannot.

Shoeing is necessary if a horse is kept or used in circumstances where the
hoof wall wears down faster than it grows. The wall has to be trimmed if it
grows faster than it wears. Neither shoeing nor trimming is necessary if the
horse鈥檚 hooves maintain correct proportions in the circumstances in which it is
kept and used. If you keep a horse, regular, knowledgeable inspection of its
feet is essential for its well-being. The decision to shoe or not should be
based on such inspection. The adage is: 鈥淣o foot, no horse.鈥�

John Somerwill

Bacup, Lancashire

Answer: The practice of shoeing horses goes back as far as the Romans, who
used tie-on horseshoes called hipposandals. Horses are not the only animals to
be shod in some fashion. Humans have also produced shoes for draft oxen and sled
dogs, not to mention shoes for themselves.

Kirstin Darke

Christchurch, Dorset

This week鈥檚 questions

In the dock: Why are dock leaves so effective at relieving stings from
nettles? Are they effective on any other plant or insect stings? Is this how the
name is derived?

Tim Crow

Highnam, Gloucestershire

Forest of fear: I read recently that oak and fir trees are far more likely to
be struck by lightning than pines, and beech is the tree least likely to attract
a lightning strike. Does anyone know if this is correct and, if so, why?

Jeff Kessler

Leeds, West Yorkshire

Pain transfer: Recently I had an itch on my right forearm. I scratched it
hard with a sharp left fingernail. While experiencing the usual momentary
ecstasy of an itch well scratched, I concurrently felt a 鈥渟tabbing pain鈥� just
above the waistline at the left side of my back. The more vigorously I scratched
my arm, the more intensely I felt the sympathetic stabbing in my back.

A few days later I found the scab I had created on my arm and attacked it
again, and found that the exact same point on my lower left back was being
stabbed once more. Why?

Barrie Snell

Southsea, Hampshire