Negative ion filters create ozone -- smells fresh BUT ozone is very hard
on the lungs.  Stick with hepa filter air cleaners.  Don't take my word
for it; ask a pulmonologist or an allergist.  Ozone is great way up in
the ozone layer, but generating it at home amounts to creating your own
localized good smelling pollution.
 
Litter: not familiar with that one, but if it is a clumping litter do
take into account if your ferrets ever dig and snorkel in their litter,
if they ever have discharge, if they ever wipe themselves in their
litter, of if they ever have rectal prolapses because clumping litter
can cause problems (some serious).  (BTW, Mornie, loves Leo Kottke's
song "Snorkle"
http://tingilinde.typepad.com/starstuff/2004/02/the_leo_and_mor.html .)
 
Deafness:
http://wolfysluv.jacksnet.com/deaf.html
[Posted in FML issue 4553]