In Norse mythology, Nidhogg ("tearer of corpses") was the monster that ate the roots of the World Tree, Yggdrasil and swore at the eagle living in the tree's branches. Nidhogg also ate corpses.
... that Vronsky is about to propose to her.
The following morning Stiva and Vronsky are at the station to welcome Anna and Vronsky's mother respectively. This is ...