Every so often, our fur covered slinkies remind us that their anscestors
were predators.  The cannibalistic behavior your friend noticed is not
unusual with carnivores (I've seen it in cats, and heard of it happening
with canines and other carnivores as well).  Still born kits represent a
significant energy/protein source that doesn't have to be hunted down, and
is immediately available for an animal that needs that food source, in the
wild.  Also, it may relate to nest cleaning (ferrets, like cats, will go so
far as to eat the fecal matter of their young, to keep the nest clean.  Such
behavior most frequently occurs with novice mothers.
 
As I'm sure you've noticed by now, a great deal of ferret behavior is
'hardwired' into the system, not learned.  This is part of that hardwiring
that hasn't been bred out yet (no reason for the breeders to select against
it).  Most of the time, our Significant Otters are unending sources of joy,
but occasionally, we are rudely reminded of thier animal side.
[Posted in FML issue 1528]