One thing when testing hearing; The "test" shouldn't be moving or send out
a vibration through the floor.  Either of these could give you a false
positive.
 
How I test; I use an empty paper towel tube (the big poster tubes work the
best) and "trumpet" through it as loudly as possible.  Any ferret who could
hear it either runs like the dickens, immediately pounces, or will freeze
until it hears it again.  Be sure to direct the tube away from the ferret,
for two reasons; 1) So the they don't feel the air flow. 2) So they can't
run up the tube (if you use the large poster tubes) and bite your lips.
 
SP
[Posted in FML issue 2779]