One thing about hogs is they get dumb when feeding. They are so preoccupied while their nose (best sense is smell hands down) is buried and busy in the feed source...
You mean that they suffer attention anosmia as well?
See this thread for attention blindness... http://thefiringline.com/forums/show...tion+blindness
I would also add that sounders apparently feel much more secure or preoccupied when operating as a larger group. I have come across a couple that did move away from me, but really didn't change their browsing behavior or speed, just direction after individuals stopped, saw me, and then continued in a different direction. One group had an individual challenge me with a faux charge and stayed between the group and me, but the group operated as if oblivious to my presence.