I had a lab that was about as gentle and non agreesive as they come ,at least i thought she was until we came across a crippled doe in a cornfield while hunting pheasants. In nothing flat she turned into a very vicious and blood thristy critter and I had to use the shotgun butt to beat here of that deer.

Besides , it is common knowledge that many dogs that are household pets become cold blooded killers if they get a chance to run deer.