Those are "soft spots" for humans that will elicit a take down the fastest. Animals instinctively know this and will do the same to other animals, as well. You'll actually see they are going for lower torso when you see them going for the genitals. With the face, they are attempting to cut off breathing. After the take down, you'll see the animals go for a person's neck, then belly.
I'm watching that too! Maybe the person ends up looking them in the eyes and the animal takes that as a threat or maybe its because the face is a vulnerable spot and the animal is aware of that. As for the genitals, I'm not sure on that one.