  We examine the origin of possible failures of the quark-hadron local duality.
In particular, we consider a correlator of two currents comprising heavy quark
operators, and compare the evaluation by the Operator Product Expansion with
the result obtained inserting an infinite set of hadronic states, in the N_c to
infinity limit. Whereas the smeared spectral functions agree with each other,
their local behaviour is different. The difference manifests itself in the form
of a term O(Lambda/epsilon) (epsilon being the residual energy) that is not
present in the expansion in powers of Lambda/epsilon predicted by the OPE.
