  We study brane inflation scenarios in a warped throat geometry and show that
there exists a consistency condition between the non-Gaussianity of the
curvature perturbation and the amplitude and scale-dependence of the primordial
gravitational waves. This condition is independent of the warping of the throat
and the form of the inflaton potential. We find that such a relation could be
tested by a future CMB polarization experiment if the Planck satellite is able
to detect both a gravitational wave background and a non-Gaussian statistic. In
models where the observable stage of inflation occurs when the brane is in the
tip region of the throat, we derive a further consistency condition involving
the scalar spectral index, the tensor-scalar ratio and the curvature
perturbation bispectrum. We show that when such a relation is combined with the
WMAP3 results, it leads to a model-independent bound on the gravitational wave
amplitude given by 0.001 < r < 0.01. This corresponds to the range of
sensitivity of the next generation of CMB polarization experiments.
