Dog Shaking With His Head

At the opposite end of the scale, the largest dogs and large mammals such as bears shake as slow as 4 hertz or four complete shakes per second.
Conclusions
The studies suggest that somewhere along the evolutionary line, that most animals learned to shake at an optimum frequency to remove water from their coat. It can now be understood that while most owners hate it when dogs shake water inside their house, that dogs are just performing an automatic survival function.