Dog Shaking With His Head

“The scientists determined that shaking begins at the head area, which provides a solid point for the energy wave to propagate down the animal's body. The head can also twist more, resulting in higher amplitude waves. Once that process starts, the animal's head, body and skin all move during a shake”
The body shakes at the same frequency as the skin but it cannot rotate as far. This means the skin twists further around the body and moves faster than the body and head causing a higher acceleration and higher water removal. On some animals the skin can move up to 90 degrees on either side of the spine.
Dogs that have a lot of hair/ fur often have loose skin that further assists the acceleration of the coat when the dog changes the direction of its shake.