Although every single episode features violence, it can sometimes be graphic and even excessive. Some notable moments from each season...
Episode 1 Days Gone By: Various dead bodies and violently deformed walkers are seen throughout the episode. At the end of the episode, a horse is ripped apart and eaten alive by walkers. Very graphic and disturbing, especially for animal lovers. The horse's organs are later seen being ripped out and eaten by a horde of walkers.
Episode 2 Guts: The main characters chop a walker up and smear it's blood, tissue and organs over themselves in order to smell dead to get through a horde of walkers. Very graphic and bloody.
Episode 3 Tell It To The Frogs: A deer's neck is seen torn open and being eaten by a walker. Mostly blood, but still gory. The walkers head is then smashed in. Later in the episode, a man strikes his wife. Shane then proceeds to beat the abuser's face until he is unrecognizable.
Episode 4 Vatos: The camp is attacked by walkers; a character is seen being partially eaten. Violent walker and character deaths (throats being ripped out, flesh being torn). In the aftermath, we seen a very mutilated body of a character, who's wife then stabs his head repeatedly with a pickax to make sure he doesn't come back as a walker (very gory, could be disturbing).
Episode 5 Wildfire: In the aftermath of the previous episode's attack, characters "put down" the corpses by stabbing them in the head. Carol takes a pickaxe to her late abusive husband's head over and over until the dead man's head is a smashed pile of brains and gore.
Episode 1 What Lies Ahead: A horde of walkers makes the group hide under cars, one gets trapped in the RV and must repeatedly stab a gruesome and frightening walker in the head with a screwdriver repeatedly. Two main characters kill and cut open a walker to check the contents of it's stomach. Graphic and bloody.
Episode 2 Bloodletting: A child has bullet fragments removed from him. He screams in pain and passes out. The scene could be upsetting for some people.
Episode 3 Save The Last One: A man shots another man in the leg to leave him as a distraction for the walkers so the other can get away. We see the man's ear being ripped off and chunks of his flesh being torn away as walkers eat him alive.
Episode 4 Cherokee Rose: A walker is stuck in a well and might contaminate the water, so they life it out with a rope around it's middle, which causing it's body tear in half. Extremely graphic, gory and bloody; this scene made the show infamous for it's violent content. Also, a walker attacks a woman in a pharmacy and a man hits it with a wooden plank, causing it's head to almost separate from it's neck but not completely. The man smashes it's head in repeatedly.
Episode 9 Triggerfinger: A walkers smashes it's face through a car windshield to try and get to an injured person; the skin on it's face gets peeled back by the broken glass, very bloody. A man's leg gets impaled by a gate spike.
Episode 1 Seed: A man's leg is chopped off with an axe.
Episode 2 Sick: A man kills another man with a fireplace poker. The murderer is later killed with a single machete chop to the forehead.
Episode 4 Killer Within: A pregnant woman goes into labor during a zombie attack. She has another woman cut her baby out of her. We see the blade slicing the pregnant belly.
Episode 8 Made to Suffer A man breaks the bone out of a zombie and uses it to stab another man in the neck. Later, a woman stabs a man's zombified daughter in the head (very gory), and this leads to a brutal fist fight between them in which she gouges his eye out with a shard of glass.
Episode 10 Home: A woman tackles a zombie, chops it's arms off with an axe, and (in close-up) curb stomps it's head against a rock. We see it's teeth pop out and it's jaw dislodge in the close-up.
Episode 13 Arrow on the Doorpost: A zombie's head is crushed against a wall graphically with a baseball bat.
Episode 16 Welcome to the Tombs: A man mows down a group of innocent people with a machine gun and then proceeds to shoot them one-by-one in the head with a pistol until he runs out of ammo. The scene is more disturbing than it is graphic.
Episodes 1-5 of the season revolve around a virus that causes people to bleed out and turn into walkers. Many shots of people choking on blood, bleeding out their eyes/ears/nose/mouth, and in some cases turning and biting survivors.
Episodes 6-7 of the season revolve around the Governor in the six months between seasons three and four. We see him interact with a group of survivors. He kills a man turning into a walker with an oxygen tank. He also protects a little girl by killing a walker by tearing it's jaw off with an object.
Episode 8 Too Far Gone: A man kills an elderly man with a sword by chopping his head off in a series of slashes. We see the victim try to crawl away, but he is held down and decapitated. In reaction to this, Rick fights the murderer in a very realistic fist-fight. Rick's injuries from the fight can be upsetting to some viewers.
Episodes 9-13 revolve around different groups of survivors wandering for a new sanctuary. They encounter countless zombies. Each episode features some form of zombie violence.
Episode 14 The Grove: This episode features subject matter involving a mentally deranged child committing acts of violence. A little girl murders another child, and attempts to kill a baby, and in response to this an adult shoots her dead.
Episode 16 A: This episode features a sequence in which a group of marauders attack's Rick's band of survivors. A man threatens to rape Carl and Michonne. Rick frees himself by biting the man restraining him in the nick and tearing out the jugular (we see Rick spit it out too). Once freed, Rick repeatedly stabs the rapist to death. Also, this episode (in it's final moments) introduces the theme of cannibalism into the series.
Episode 1 No Sanctuary: The opening sequence of the season shows the cannibals bleeding out humans over a trough by clubbing them with a bat and slicing their throats. Also, a human meat locker is shown briefly.
Episode 3 Four Walls and a Roof: A man sees cannibals eating his leg in front of him. The cannibals later go to attack Rick's group, and Rick and his band of survivors viciously slaughter them with bladed and blunt objects inside a church.
Episode 4 Slabtown: A woman, although she protests against it, is held down and has her arm amputated with a razor wire. Very disturbing and gory.
Episode 7 Crossed: Rick and survivors enter a part of Atlanta that was previously napalmed. Bodies of the victims can be seen melted against the pavement. Some of them are now walkers. Daryl tears the head off one of them and uses it to beat an attacker. (The entire sequence isn't so much as gory/violent as it is just plain gross.)
Episode 8 Coda: Rick drives a car into an escaping man (with his hands tied). The man breaks his neck, but survives being hit with the vehicle. Rick approaches the pleading man and shoots him in the head (off-screen). Later in the episode, Beth is shot in the head. The scene is very sudden and may be shocking to some viewers (but, overall, not "graphic" by this show's standards).
Episode 9 What Happened and What's Going On: Tyresse is bit and has his arm amputated. There are several scenes in which people who have died in the past are seen in hallucinations, still with their fatal injuries. Lots of injury detail shown, including pooling and dripping blood.
Strong sequences of graphic violence and horror throughout.
A variety of weapons are used to kill zombies, from guns to axes, and have bloody results.
Throughout the show many zombies are seen in various states of decay, sometimes with bone or internal organs are exposed.
The series has a focus on what humanity is left in a world after humanity is extinct. As the series progresses violent conflicts between people begin to arise.