  Zitterbewegung of massive and massless scalar bosons and a massive Proca
(spin-1) boson is analyzed. The equations describing the evolution of the
velocity and position of the scalar boson in the generalized Feshbach-Villars
representation and the corresponding equations for the massive Proca particle
in the Sakata-Taketani representation are equivalent to each other and to the
well-known equations for the Dirac particle. However, Zitterbewegung does not
appear in the Foldy-Wouthuysen representation. Since the position and velocity
operators in the Foldy-Wouthuysen representation and their transforms to other
representations are the quantum-mechanical counterparts of the corresponding
classical variables, Zitterbewegung is not observable.
