The surprising thing was the dog’s body language; it approached the child without apparent hostility, as though it just wanted to sniff him and, possibly, play with him. Then, when it got close enough, WHAM!!, it went into full wolf/predator mode. Never was a dog so deserving of its end as that one. BTW, I’m dog daddy to two big, friendly dogs, an 85 lb. Pitador and a 110 lb. Great Dane.
I may be mistaken, but it looked to me like the dog was stalking the child from the get-go. The fact that dog apparently tried to hamstring the child leads me to believe that he saw the kid as lunch.