When I was a young kid my folks got me a Shepard/Collie mix that went about 45 lbs. One day a traveling salesmen came knocking and that dog just about went through a wood framed screen door after the guy. Dude promptly left. Kinda freaked my mom out, the dog lived to be 18 and never acted aggressive towards another person. Mom always believed the guy must have been bad news and that dog knew it.
Could very well be the case.
