How is the ferret in "Sredni Vashtar" linked to death?
The ferret is linked to death for its part in the killing of Mrs. De Ropp, Conradin's guardian.
In the story, the ferret is a symbol of autonomy and dominance. It isn't interested in being thwarted for its own good nor is it engrossed with the prospect of bowing to the whims of a mercurial (temperamental) guardian. Conradin "worships" the ferret, because its very fierceness and independence encapsulates everything he wants to be.
When Mrs. De Ropp threatens to dethrone his god, Conradin prays to Sredni Vashtar for deliverance. In his hymn of deliverance, he besieges the ferret to proudly bring death to those of his enemies who call for peace. Thus, this improvised hymn foreshadows the ferret as a figure of death. So it is that when Mrs. De Ropp enters the domain of the ferret god (the shed), she is never seen alive again. The ferret emerges with "dark wet stains around the fur of its jaws and throat"; as an avenger of the oppressed, Sredni Vashtar is the harbinger of death.