BBC Focus

Snakes don’t have claws or powerful

jaws to pin down their prey. If the

venom doesn’t kill quickly enough, the

victimmayescapeintoaburrowor

upatreeanddieoutofreachofthe

snake–or,worse,injurethesnakein

its death throes.

Snakes are in an evolutionary arms

race with their prey, which are

evolving ever-greater resistance to

snake venom. Snakes have adapted to

thisbyevolvingvenomsthatcontaina

cocktail of several hundred different

enzymes and proteins. Some block

nerve transmission, others interfere

How does snake venom kill so quickly?

JORDAN SHEMILT, MIDSOMER NORTON

with the beating rhythm of the heart,

some break down muscle tissue or

cause blood vessels to suddenly

become leaky.

Snakes can control how much venom

t hey inject wit h a single bite a nd

generally use far more than the lethal

dose. The black mamba, for example,

injects up to 12 times the lethal dose

for humans in each bite and may bite as

ma ny as 12 times in a single attack.

This mamba has the fastest-acting

venom of any snake, but humans are

much la rger t ha n its usual prey so it

still takes 20 minutes for you to die. LV

There are plenty of theories for why

people start nail-biting (or what

doctors call ‘onychophagia’),

including perfectionism and stress.

And there’s also the Freudian notion

t hat it’s to do wit h being stuck at t he

oral stage of psychological

development! But as to why nail-

biting is so addictive (20 to 30 per

cent of us do it), t here’s little resea rch.

We ca n speculate t hat it is to do wit h

its cost-free ease, practicality and

relative social acceptability, a nd

there’s the rewarding aspect of

getting each nail just how you want

it. On a positive note, childhood

nail-biters are less prone to allergies,

presumably because they’re exposed

to more germs. CJ

Why is nail-biting so

addictive?

MADISON HUGHES, SHROPSHIRE

Can you die

from a

nosebleed?

KADIM OLZHAS, KAZAKHSTAN

Most nosebleeds involve superficial
bleeding from the capillaries close to the
skin and can be stopped with pressure
and an ice pack. But nosebleeds can also
be caused by a tor n inter nal ca rotid a r ter y
and in that case the bleeding can be fast
enough to be life t h reatening. It’s also
possible for a milder nosebleed to block
your airway and asphyxiate you.
A 47-year-old man from Gravesend, Kent
died this way in 2011. LV

Don’t pick a fight

wth this fella