Pigmen aren't intelligent. They are just like any other friendly mob, but when you attack one, the "Angry" variable for all close by pigmen is changed to 1, making them attack you. Trust me, I've observed their coding.
I agree with this, but with one variation: it seems the "Angry" variable of all pigmen in the area flip when any one of them is directly attacked. By the way, they never begrudge an "accidental" barbecue, just light the floor under them. They seem to assume it's a regular hazard of the Nether.
I've got 2 suggestions for expirements that test the basic movement for the pigmen.
Use an enclosed room, no possibilities for ghasts to either get in or shoot out the walls, etc. Make the room slanted, with a flat ground on both the top and bottom (like _/¯ , but not as steep in the middle). This could be used to see if there is a preference for height.
Find a deep cubby hole of medium or large size. Near the entrance, build a shelter with an entryway in the back, facing the inside of the cubby hole. Something like this (ignore the .'s, they are only for spacing):
| . |¯¯|
| . .¯ .|
|. . . .|
Get some ZPs to crowd around near where the shelter is, and wait for a ghast to come within range. See if the ZP's actually try to path in to the shelter, or if they just run to the back of the cubbyhole.
You guys need to make the same experiments with others mobs, like cows, pigs, because this way you are making conclusion on its actions, but you guys don't know how diferent they are from the other mobs, this need to be tested too
I've read through the entire thing here, good. However, I'm sad that Apv left, I'd have liked to see those research documents D:
Nontheless, here I am. Don't expect an application, because I can't test.