  We study the topological entropy of chaotic repellers formed by those points
in a given chaotic attractor that never visit some small forbidden hole-region
in the phase space. The hole is a set of points in the phase space that have a
sequence $\alpha=(\alpha_0\alpha_1...\alpha_{l-1})$ as the first $l$ letters in
their itineraries. We point out that the difference between the topological
entropies of the attractor and the embedded repeller is for most choices of
$\alpha$ approximately equal to the Parry measure corresponding to $\alpha$,
$\mu_P(\alpha)$. When the hole encompasses a point of a short periodic orbit,
the entropy difference is significantly smaller than $\mu_P(\alpha)$. This
discrepancy is described by the formula which relates the length of the short
periodic orbit, the Parry measure $\mu_P(\alpha)$, and the topological
entropies of the two chaotic sets.
