2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/222069Unstable modes growing when two plasma shells cross over a background plasma at arbitrary angle $θ$, are investigated using a non-relativistic three cold fluids model. Parallel flows with $θ=0$ are slightly more unstable than anti-parallel ones with $θ=π$. The case $θ=π/2$ is as unstable as the $θ=0$ one, but the fastest growing modes are oblique. While the most unstable wave vector varies with orientation, its growth rate slightly evolves and there is no such thing as a stable configuration. A number of exact results can be derived, especially for the $θ=π/2$ case.4 pages, 3 figures, to appear in Phys. Lett. APlasma PhysicsSolar and Stellar Astrophysicstext