There are what we call 'zombie animals' that already exist in nature. Some great examples are Zombie Snails; snails that are infected with a parasite that takes control of the snail's brain, causes the snail to climb up in a tree in the open where it never normally would go, and the snails tentacles pulsate and become huge. Birds see that, think it's a caterpillar, and literally attack the snail, bite the tentacles off so the parasite is able to then be inserted inside the bird where it reproduces. Another great zombie animal are Zombie Ants. Zombie ants are infected by a fungus that takes control of the brain; causes the ant to climb out into the sun. The ant then dies and the fungus grows out of the ant.
Possibly the most disturbing example of zombie animals is the Zombie Cricket; crickets that are infected with a parasitic worm. The worm grows to adulthood inside the cricket, and then when the worm needs to get out of the cricket to go mate, it takes control of the cricket's brain, causes the cricket to find a body of water, jump into that body of water. Crickets can swim, they normally would never go into water, and the cricket drowns in the body of water. As the cricket's drowning, the worm exits the cricket, but the horrible thing is the worm is 10 times longer than the cricket. You see this little cricket and this giant worm coming out of it as it drowns. Totally disgusting.