I am use to watching a lot of horror/slasher films when younger so the grossness of District 9 never really sinks in where the scenes in Antichrist leave a much more lasting impression as it feels like you are watching this happen to another person while watching it. I get a very uncomfortable feeling while watching Antichrist just as I would if I was watching something like Irréversible. Though I really enjoyed District 9, it does not give me that kind of reaction at all.
Also, I sometimes ate cat food when I was very young so maybe I do not find their eating habits too extreme. Though, I only liked the crunchy kind.