  We investigate brane inflation driven by two stacks of mobile branes in a
throat. The stack closest to the bottom of the throat annihilates first with
antibranes, resulting in particle production and a change of the equation of
state parameter w. We calculate analytically some observable signatures of the
collision; related decays are common in multi-field inflation, providing the
motivation for this case study. The discontinuity in w enters the matching
conditions relating perturbations in the remaining degree of freedom before and
after the collision, affecting the power-spectrum of curvature perturbations.
We find an oscillatory modulation of the power-spectrum for scales within the
horizon at the time of the collision, and a slightly redder spectrum on
super-horizon scales. We comment on implications for staggered inflation.
