  In arXiv:1911.06042v1 M. Casiulis et al. study a Hamiltonian model in which
rigid rotations of moving clusters give rise to scale-free correlations of
velocity and speed. M. Casiulis et al. compare correlations in their model to
those observed in real flocks of birds and claim that rigid-body rotations
provide an explanation that stands in contrast with, and it is simpler than,
previously proposed explanations of correlations in bird flocks, namely
Goldstone modes in the velocity orientations and marginal (or near-critical)
modes in the speed. Here, we show that the rigid rotation scenario is
completely inconsistent with a large body of well-established experimental
evidence on real flocks of birds, and it therefore does not provide an
appropriate explanation for the observed phenomenology.
