  We discuss basic expressions and interrelations between various physical
quantities describing the fluctuation-electromagnetic interaction of a small
polarizable particle during relativistic motion relative to the blackbody
radiation, namely tangential radiation force, rate of heating, intensity of
thermal radiation/absorption, the change of the rest mass of a particle, and
acceleration. We obtain an explicit formula for the frictional force acting on
the particle in its rest frame and discuss its connection with the particle
acceleration and the tangential force given in the reference frame of
background radiation. The criticism of our previous results in recent paper by
A. I. Volokitin (Phys. Rev. A81, 2015, 032505) is refuted.
