In a live seal, these bones, called nasal turbinates, are
covered
with a fine tissue, rich with blood vessels. Warm blood pumped through
these
vessels heat cold air before it enters a seal's lungs. When the seal
exhales, the same tissue captures warmth from the animal's breath (and
also
traps precious moisture that would otherwise escape). This evolutionary
trick for conserving energy is called nasal counter-current heat
exchange.
