Facts
 
 
It
is
impossible
 
to
lick
your
elbow.
You
cannot
hum
 
if
you
are
holding
your
nose.
 
No-one
is
entirely
sure
why
duck
quacks
 
produce
no
echoes.
You
cannot
sneeze
 
while
you
have
your
eyes open.
Guinea pigs,
 
it
seems,
are
unable
 
to
sweat.