Abstract
Chaotic attractors containing periodic orbits with different numbers of unstable directions display fluctuating Lyapunov exponents. We show that the existence of certain nonattracting chaotic sets inside the attractor guarantees the occurrence of this behavior in a persistent manner. These nonattracting sets can be brought inside the attractor via a new type of crisis and may be created, as a parameter is varied, via a sequence of bifurcations out of unstable periodic orbits.