That confrontation just before the scene with the bear. And of course, the bear itself.
In particular, right after Amos wounds the bear's shoulder. It roars in pain, then looks down at Amos with a Slasher Smile that the Joker would be proud of.
The confrontation between Tod and Copper at the den. You want to see what a realDeath Glare looks like? That kind of snarl is what an animal does when it intends to defend something to the death - and no less.
The look on Copper's face is no better. Let's put it in perspective—he spent the better part of the movie looking like a happy, lovable non-anthropomorphic Goofy. Then shit happens, he blames Todd for it, and now he's looking like a straight-up Hell Hound as he tries to drag his former friend out of his own home and kill him.