We study vulnerability in the BZ reaction using experimental and
numerical methods.  We show that the width of the vulnerable window
(VW) decreases with increasing velocity of wave propagation.  Detailed
study of the structure of the VW revealed a new effect: the
development of multiple responses to a single premature stimulus; a
single premature stimulation in a homogeneous one-dimensional medium
generates two or three propagating waves.  We locate this effect in the
parametric space and discuss its mechanism.