I don't get the extra damage thing........especially if your hitting the opposite shoulder ! From my experience about 1.5" under the entry the blades open fully...........and a huge cut is made......say through both lungs ! If both lungs are collapsed they are collapsed........aren't they ? I don't see how any additional damage can be done !!

However.........just like with a lot of heads......you probably won't find much blood ! That's happened to me with Spitfire's and Muzzy's without an exit wound !!