It's clear from the very beginning that the Machine is an industrial slaughterhouse. But for much of the game, you are exploring the engines and boilers that make the factory work, not the slaughtering floor itself. It isn't until the very end that you reach the Pigline, where you see not pigs, but dozens of human carcassas suspended by meat hooks and sliced by enormous mechanical butchers. The sheer scope of the slaughter going on is made apparent in the Tripery, where you see ground human flesh pushed through pipes like sausage, and are forced to wade through an ocean of blood and body parts.
One of monsters nicknamed "Mr. Piggy", it looks like some sort of mix between human and a pig. It produces a loud noises whenever it's around, and is capable running really fast, being able to catch up with you quickly.
Unlike the previous games, where there were a few music and sound cues, there is none of that, making it harder to tell where the monster is. Oh yeah, and your lantern starts flickering when it's near by, making it harder to see.
They are also implied to have a child-like mentality, since one of them is shown in it's cell playing with blocks. This is both dissonant, considering they are trying to kill you throughout the game (and for good reason), and a bit sad. Also a bit of a Tear Jerker.
The sewers part is pretty scary especially for people who played the first game. Why? Well, the infamous water monster appears again. As well as a manpig.
It's not a cage, per se. Most of the beds in the manor have been fitted with bars for some reason, inducing plenty of Fridge Horror. Are they meant to contain the sleepers or protect them from something that stalks the corridors at night? It's to capture Mandus's rich guests and tip them straight into the Machine with an ingenious hydraulic system.
The Manpigs invasion of London. Through this level you run terrified through the burning slums of the east end, houses aflame, explosions and gunshots blasting in the distance, people screaming and running all around you as the hordes of Manpigs butcher or abduct men, women, and children without mercy.
Fridge Horror makes this even worse; considering how one of the overarching themes of the game is the dark nightmares of the twentieth century and how we are near the centential of World War One. Having a huge section of London's capital gutted could cause all kinds of problems in the face of less benevolent powers like Imperial Germany, in addition to demonstrating publicly how Alexander's tools could be used by normal humans. Mandus, did you just make the 20th century even more horrifying than it was?!?
Throughout the game you see the ghostly figures of Mandus's twin sons running through the house and factory, never once showing their faces (which in itself is highly unnerving), but when Mandus is tricked into restarting the machine they appear inches from the camera their faces covered with blood, terrifying slasher smiles on their lips, and in the process of ripping their own hearts out of their chest.
That vaguely aztec-like pig mask? It follows you.
The mask cannot be interacted with directly, though you can throw things at it. So what does it mean when you see it sitting on a chair, you turn your head to look at the rest of the room without touching anything, and when you turn back it's on the dresser instead? This is one of the first unusual things that can happen in the game.
The electric pig scenes. Oh god the electric pig scenes. You enter a room full of floor-to-ceiling tubes and the lights go out. Then you hear a crackle of electricity . . . and a Manpig covered in blue sparks starts lumbering toward you. This is all in near-total darkness. You have to turn the lights back on to escape.
The second scene is worse. There's not one, but two electric Manpigs, and you don't have an option to turn the lights back on; you just have to run for your life.
The reoccurring painting of a woman wearing a crazed expression on her face, brandishing a knife besides her head and carrying a baby in her lap (if it is a baby at all). An infant leg is seen sticking out of a cauldron next to her.