Now it makes sense..
that long fur i had found, and the abces.
2 bite marks, about half a cm apart.
Mice or rats don't bite that way, nor do they have long hair.
But a Ferret, does have all those things.
And a bite from a Ferret, would most likely introduce bacteria that Boris had not yet encountered before while fighting with other cats, or killing mice...
Boris is mental, to go after ferrets...they are viscous little buggers in their own right.