You were a werewolf, searching for food in the forest. You use your great sense of smell to find berries when suddenly you pick of a smell of blood.. you send a rat on the ground.

The rat was drained of its blood. Strange. And there seemed to be a trail of other animals who suffered the same fate. You follow the trail, thinking that it was some bigger animal. Curiously

At the end of the trail, in a forest clearing, you see a vampire. Sucking the blood out of a human.