  It is demonstrated that the candidate tetraquark states $Z_b(10610)$,
$Z_b(10650)$, $Z_c(3900)$, and $Z_c(4025)$ are coupled channel cusp effects.
The model explains in a natural way the masses and quantum numbers of the
putative states and the near equality of the widths of the $Z_b$ states. It is
argued that the $Z_c(3900)$ and $Z_c(4025)$ should be visible in $\bar B^0 \to
J/\psi \pi^0\pi^0$ or $B^- \to J/\psi \pi^- \pi^0$, but should {\it not} appear
in $\bar B^0 \to J/\psi \pi^+\pi^-$, in agreement with recent LHCb results.
Additional tests for cusp effects are suggested.
