  We report on a series of measurements aimed to characterize the development
and the dynamics of the rhythmic applause in concert halls. Our results
demonstrate that while this process shares many characteristics of other
systems that are known to synchronize, it also has features that are unexpected
and unaccounted for in many other systems. In particular, we find that the
mechanism lying at the heart of the synchronization process is the period
doubling of the clapping rhythm. The characteristic interplay between
synchronized and unsynchronized regimes during the applause is the result of a
frustration in the systems. All results are understandable in the framework of
the Kuramoto model.
