Wyoming resident here. Every one knows that a bear will kill you in an instant, but if you're up here for the summer, for the love of god please stay away from moose. Moose get really territorial, they are almost as tall as a house, and they will fuck your shit up. Moose are chill, until they are not.
PS: Don't approach bison (buffalo), or any wildlife, in Yellowstone you big fuckin' dummy.