I’ve seen a lot of good theories from what the monsters from ‘From’ are [I call them the Walkers for ease of note taking], and while I do love the ‘they used to be human’ theory, I don’t think its correct. In fact, I think it’s the inverse.
I think these things are just monsters. They aren’t human, they never have been, but they’re trying to be. Trying to learn. They aren’t trying to integrate into human life - no, they will continue to kill the townspeople even if they succeed, but they’re just curious.
They have hunted and killed these people and they’re getting curious on what they are. So they begin to take them apart more medically. It’s why all the corpses in the town have their organs gone, cleanly removed, because the Walkers are taking the puzzle apart to see how the pieces fit. They don’t eat the bodies, so why leave them once the fun is over? Might as well learn a bit.
And we see them mimic human behavior too. At first it seems like they only do it to fool humans, but they do it alone too. Their private den is full of used human toys, toys they’ve been playing with. The walls are drawn on in crayon, learning from Victor and his drawings all over the town.
Smiley and ‘Jasmine’ both show this behavior well, taking time to deviate from killing just to do small human pleasures. Jasmine cleans her dress despite knowing it will be coated in blood soon, and Smiley wastes time while hunting just to sit in the bus and pretend to drive it, just to see what it feels like to sit in a car.
They’re not properly ‘understanding’ emotions, or actions, or any of what they’re mimicking - they’re just trying to copy it. They think humans are neat little creatures, and they wanna be in on the fun.