taken from a thread with similar topic
from boy in blues:
both guys and gals shiver only
after urinating and not during urinating because even though the
body loses heat when warm urine is transferred out, the body also
loses total mass in the form of urine when the bladder squeezes it
out. it is only after urinating, the bladder has squeezed out most
of its contents that the bladder relaxes, allowing atmospheric
pressure to cause cool surrounding air to enter through the uretha
and expand the bladder to its relaxed volume. shivering is caused
by this sudden entrance of cool air into the body causing heat to
be quickly transferred from the body to warm the bladder air to
body temperature.
