  To assess how anisotropic transverse flow is created in a system out of
equilibrium, we compare several kinetic-theoretical models in the
few-rescatterings regime. We compare the flow harmonics $v_n$ from three types
of transport simulations, with either $2\to 2$ or $2\to 0$ collision kernels
and in the former case allowing the particles to rescatter several times or
not, and from analytical calculations neglecting the gain term of the Boltzmann
equation. We find that the even flow harmonics are similar in all approaches,
while the odd ones differ significantly. This suggests that while even $v_n$
harmonics may to a large extent be due to the anisotropic escape probability of
particles, this is not the predominant mechanism underlying the odd $v_n$
coefficients.
