Nodes can swell in response to infection or to lymphoma, BUT some rare
ferrets just have "popped nodes", i.e. ones which sit high up (Have had
one, Meeteetse, in 23 years who was like that.), and many ferrets have
pronounced fat padding around nodes.  The firmness can sometimes help
your vet figure if the nodes are swollen or cushioned.  If there is a
question your vet might want to wait and observe, or do an aspiration, or
pull a node, or try treating with a broad spectrum antibiotic, depending
on the situation on examination.
[Posted in FML issue 4573]