It's a good idea to give your ferrets a general check-over from time
to time.  This should not substitute for the annual vet visit [9.4],
but you might notice something before it gets bad.  Anytime you notice
anything unusual, take the ferret to the vet.

Start by checking your ferret's ears, which should look clean and
pink.  If you see wax, clean them.  If the wax is black or has dark
flecks, the ferret might have ear mites [10.10].  Check the cartilage
for swelling or distortion.  Check the ferret's eyes, which should
look clear and alert, with no films or discharge.  (Ferrets do have a
"second eyelid" which might appear as a bluish-white rim around the
edge of the eye.)  Feel carefully all around the neck, throat and chin
area, looking for lumps or swelling.  Check the gums, which should be
pink and healthy-looking, and the teeth, looking for excessive tartar
or discoloration.  Whiskers should be long and strong, not brittle or
broken.

Now hold the ferret under the front legs, with the back legs on your
lap or a table.  Run your hands lightly along the ferret's body,
checking for lumps.  You can also check muscle tone and weight this
way: you should be able to feel ribs, but not see them, and the ferret
should feel firm and supple, not loose, flabby or skinny.  Pull gently
on the ferret's legs to check for lumps or swelling on the legs,
knees, or feet; the ferret should pull the legs back in.  The pads
should be pink and soft, with maybe a bit of callus, not irritated or
cracking.

Your ferret's behavior is also a good indicator of its general health.
Sleeping a lot is normal, and older ferrets will slow down a bit, but
they should always be curious, alert, and playful.  Any change in
normal habits might be a sign of a problem.