  Dark energy constraints have forced viable alternatives that differ
substantially from a cosmological constant Lambda to have an equation of state
w that evolves across the phantom divide set by Lambda. Naively, crossing this
divide makes the dark energy gravitationally unstable, a problem that is
typically finessed by unphysically ignoring the perturbations. While this
procedure does not affect constraints near the favored cosmological constant
model it can artificially enhance the confidence with which alternate models
are rejected. Similar to the general problem of stability for w< 0, the
solution lies in the internal degrees of freedom in the dark energy sector. We
explicitly show how to construct a two scalar field model that crosses the
phantom divide and mimics the single field behavior on either side to
substantially better than 1% in all observables. It is representative of models
where the internal degrees of freedom keep the dark energy smooth out to the
horizon scale independently of the equation of state.
