  We study the recent claim that black NS5-branes are filled with folded
strings. We calculate, in the near-extremal case, the number of folded strings
at the black fivebranes interior, using different approaches, and get the exact
same answer. The backreaction of the folded strings leads us to argue that the
interior of the black fivebrane is AdS_2 (times a compact manifold) and that
infalling matter cannot reach the interior, due to a shock wave at the horizon.
These considerations also suggest a novel insight into the black fivebranes
entropy.
