Consider a isolated system of particles. If no external force acts on this system, the momentum of the system should remain constant.
If the isolated system of particles represents living creature. And if we assume you (the reader) to represent that system. If you even shake your hand, you are changing the positions of the particle of your hand.
I hope, we can move the particles of hand at any speed (till the limit allowed by laws), at least to cross the initial momentum of the system. Is this not possible? If it is possible, aren't we violating the principle of conservation of linear momentum?