Possum

In a backwoods cabin, a boy called Little Man lives with his dad (a trapper), his older sister Missy, and his younger sister Kid, who is feral, spends most of her time under the table, and can imitate the sound of any animal. Their mother is dead. One day, while dad's in town selling skins, Missy teases Kid and gets bitten. There's Hell to pay when dad gets home, and Kid runs off into the night to spend it with her animal friends. Little Man, who narrates much of the story as well as his reflections in a whisper, must sort out loss and emptiness. - IMDb