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Mekong mystery

Question: My wife saw a puzzling sight in October 1994, in the Mekong River
near Nongkhai, Thailand, during a full moon, in the evening. Lights appeared
under the water for a few hundred metres along the Mekong River. They rose from
the bottom of the river and floated to the surface, then shot like missiles into
the sky and out of sight. They were the size of beach balls, and many flew out
of the water every few minutes, surfacing about 10 metres apart. I am told this
happens every year at the same time. Locals say it is caused by a serpent
releasing her eggs. Does anyone know of this phenomenon?

(continued)

Answer: I have heard of the Mekong lights, though I have not actually seen
them. I worked in this area as a geologist, and being intrigued by reports of
the lights, inquired after the phenomenon from both local farmers and
eyewitnesses. I can offer the following extra information.

The lights not only occur in the part of the Mekong River that is referred to
by your questioner but also in an adjacent area to the north, within Laos (in
this area the Mekong River forms the national border between Laos and
Thailand).

They are confined only to this small area and I have not heard of their
occurrence anywhere else in Laos or Thailand. They arise both from the river and
from rice paddies, many of which are still flooded at that time of year.

The Thai/Lao name for them is the Nekha Lights—the nekha is a large
fish which lives in the local waters and is seen in great numbers on the river
surface at certain times of the year. Perhaps this is the serpent to which the
original questioner refers. The lights are a famous and ancient annual
phenomenon in both countries, and one to which the local people attach an
important religious significance. Many Lao and Thai people travel to the area to
try to see them, although the lights vary in their intensity and in some years
are barely visible, if at all.

The lights have been filmed, and have also been shown on Thai television. The
most intriguing aspect is that they occur only once a year, during the full moon
in October for a very limited period (possibly only one night). The duration of
a display is about 30 minutes, and there was a particularly dramatic show in
1996.

Paul

by e-mail, no address supplied

Head start

Question: When pigeons walk they move their heads rhythmically and
horizontally a considerable distance, I would estimate around 5 centimetres back
and forth. Is there a biological advantage associated with this movement and, if
not, why do they do it?

(continued)

Answer: One of your correspondents appears to believe that having
stereoscopic vision is desirable for all animals whether or not they are
predator or prey, but this is clearly not the case.

For a prey animal, having all round vision is clearly superior to stereo
vision because they can see in all directions simultaneously and it is obviously
far more difficult for any predator to sneak up on such an animal.

Stereo vision is only of any use to a predator, even though it makes them
easier to sneak up on.

Stephen Forbes

Leeds, West Yorkshire

Talon teaser

Question: Fingernails appear to grow from the base of the nail to the tip.
However, they are firmly bonded to the underlying flesh.

Do they slide over the flesh? If not, and the flesh migrates to the fingertip
with the nail, what happens to it there?

Answer: Fingernails do grow from the base of the nail and move forward at
about 0.1 millimetre per day.

In the nail bed there is a layer of dividing cells. These cells attach
themselves to the nail’s undersurface and thus the nail is bound to the nail
bed.

As the nail is pushed forward by growth at the base, the cells in the
dividing layer become unbound (due to shear forces) from the dividing layer and
the nail.

As these cells become detached, other cells from the dividing layer become
attached to the undersurface of the nail. The detached free cells act as a
lubricant to the sliding nail and they end up as debris at the tip of the
fingernail. Therefore the nail, although attached to the nail bed, can move
forwards.

T. S. Dhallu

Bridgend, Mid-Glamorgan

Answer: I managed a practical test of this many years back following an
unfortunate accident in which I slammed a door on my index finger.

The nail subsequently fell off in its entirety. With the scientific gusto and
inherent curiosity of the average eight-year-old child, I made a thick pen mark
on the flesh of the nail bed at the base of the nail area and then waited for
the results.

The nail grew over the pen mark, and could easily be seen to be advancing at
a greater speed. The nail reached the end of the bed when the pen mark had only
moved about a third of the way along the nail bed. It was clear that the nail
slides over the flesh, but there is some movement of the bed as well. As a final
note, please do not try this approach yourselves. I can assure you that losing a
fingernail in the name of scientific research is a most painful pursuit.

Christopher Street

Sheffield, South Yorkshire

Answer: Close observation of my wife’s fingernails has yielded the following
results: fingernails appear in small cardboard boxes, they are made of plastic
and are bonded to the underlying flesh by strong adhesive.

David Whittle

Southampton, Hampshire

This week’s questions

Doh Tee La So Fah Me Ray Doh: After a particularly heavy night’s drinking, I
sometimes wake up to find my customary high, nasal, tenor voice (no, it’s not
very attractive) replaced by something louder, clearer and much, much
deeper—Kenneth Williams has become Barry White. This usually lasts for
several hours. Why is this, and how can I replicate the effect without
sustaining nightly brain damage?

Michael Wickenden

Craven Arms, Shropshire

Steel smuggler: As a result of a broken leg, I now have a piece of stainless
steel that runs down the centre of my femur. It is about 30 centimetres long and
1.5 centimetres in diameter. The bone and rod are held together by four screws,
each about 8 centimetres long.

The steel plate has never caused airport security alarms to go off although a
small bunch of keys that I carry has. Why?

Barrie Quilliam

Knutsford, Cheshire