  We study a theory of minimally modified gravity called cuscuton/VCDM that
propagates only two gravitational degrees of freedom. Despite being apparently
different from general relativity (GR), it is in principle possible that this
theory might be obtained via a field redefinition starting from the GR action.
This would make the vacuum theory equivalent to GR and the theory would differ
from GR only in the presence of matter. In this paper, studying the dispersion
relation of gravitational waves and the dynamics of the Bianchi-I universe, we
prove that such a field redefinition does not exist and that the theory differs
from GR already in vacuum.
