Ultimately, it's not the North America's mega-fauna that pose the most threat to zombies. In nature, there are a whole host of tiny creatures whose main purpose is to feed upon and break down the flesh of the dead: the decomposers. Zombies, with their rotting flesh, are obviously not immune to these decomposers (what do you think causes the rotting effect?), many of which are too small to see with the bare eye. Bacteria, fungi, molds, insects such as fly maggots or flesh-eating beetles, and other invertebrates, all make up nature's diminutive clean-up crew . And it can obliterate a dead body in surprisingly little time. The clumsy undead wouldn't have the dexterity to pick off these decomposers, even if they could see or feel them. It would just be a matter of time. Stripped off all soft tissue, including brains, the zombies would be reduced to hollowed-out skeletons.
The freedom struggle gives a very good example. Gandhiji, the father of the nation, started the Satyagraha at Champaran in 1917. Then after, he took years to build upon the movement, brick by brick, steadily. Mass movements were held. People from all castes and communities were mobilized. In particular, Gandhiji was careful never to engage too fast. So much so, that he suspended the Non Cooperation Movement after the Chauri Chara incident, where a violent mob burnt a police station. He realized that by being too fast, the movement would easily crumble under the weight of the powerful British. Being steady was more important than being fast, too fast. No wonder, Gandhiji was vindicated when India won the freedom at the midnight of 15th August, when the world slept and India awoke to life and freedom.