UwantME2landWHERE!
Its tricky to tell cause from effect. The second aircraft (on the left of the video) also underwent exactly what the other did. Both had main rotor strikes, and the tails wiggle the same way.
When a few feet of the main blade is lost the massive imbalance shakes the wole aircraft (and can't be seen on this video.) The massive vibration is close enough to the main rotor 1/revolution frequency that it literally shakes the aircraft apart. That tail wiggle is the first lateral bending mode of the fuselage, and is the effect of the blade strike. I don't believe the tail was struck by anything.
Your dog knows how to find the first bending mode of a captured creature, that's why he has the instinctive lateral head shake. This shake excites the creature's natural frequency, and breaks its neck, so the dog doesn't have to do as much work to get lunch. Notice how the dog's shake frequency changes with the weight of the toy, he finds the natural frequency, and dwells there. You do that too when you pick up a long stick and snap it by shaking it from one end.