[MichaelCollins]

The dummy's breasts don't seem to move in the video despite the impacts, I think they're probably made out of steel, or a very stiff rubber. I doubt they accurately simulate real breasts, I think they're on the dummy to convey femaleness.

[watwut]

They don't need to move much. The issue I noticed is that when my breasts grew, some safety belts went through throat (previously did not).

They push the belt to the side.

[MichaelCollins]

In a collision that rends a metal car frame, I think all flesh would move. Crash test dummies don't simulate this aspect of collisions.