In my experience, ferrets and iguanas don't mix (although my two sable boys
and Spike the iguana may all be playing together now at the Rainbow Bridge -
they all went there last year when they were 7 years old - I had a very
sore heart).  The iguana had a large cage on top of the ferret cage in the
ferret room and the iguana had tree limbs from his cage to the top of the
curtains, etc.  When they were all young, I looked in one day to check on
everyone and the iguana was on the floor in shock with several bite wounds
that were bleeding.  The ferrets must have tried to "play" with Spike and
when he didn't play like they did, they went on to something else.  I was
able to save Spike, but they had to have separate free roam time after
that.
 
Spike did well with the dogs, he would dig in the dirt with Minnie (before
she decided it wasn't very queenly to dig).  The cats seemed to make him
nervous.
 
Keep in mind that as the iguana grows, its tail gets very powerful and they
use their tails to whip as their defense.  I have no doubt that a tail whip
from a 3-4 year old iguana would break every bone in a ferret's body.  I
got a tail whip once when Spike was spooked and I was trying to calm him
(he was afraid of anyone with a baseball cap on - go figure) and I had a
huge welt on my leg that turned into a very ugly bruise.
 
I think Spike used to enjoy watching the ferrets when he was in his cage
on his hot rock.  He would sometimes vigorously head bob at them (choosing
them off in iguana language).  He also used a litter box (I don't know if
the ferrets taught him this, but it was great).  They also liked to eat
each other's food.  The iguana would eat the ferret kibble when he was
roaming the floor (no ferrets in the room), and the ferrets would beg for
Spike's green beans and watermelon when I fed him.
 
That was my experience with mixing the two.  Hope this helps.
 
Buffy and Toeby's Mom
[Posted in FML issue 2666]