To me they seem "smarter."
I was playing on the Junkyard level, and on Casual you can shoot a guy, then go down the ladder and just sit there as they all come down the ladder you just went down.
On realistic, I shot the guy and went down the ladder to see if they would still follow. One did, and then I heard a person coming down the ladder. Look and there is no one there...figure it was nothing. I hear it again and again, and start getting confused because there is clearly no one coming down the ladder.
I then turn around, complete forgot there was another ladder on the other side of the hall and there are three or four guys standing there and they all open up and light me up.



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