  In this paper, I give a pedagogical discussion of the GSI anomaly. Using two
different formulations, namely the intuitive Quantum Field Theory language of
the second quantized picture as well as the language of amplitudes, I clear up
the analogies and differences between the GSI anomaly and other processes (the
Double Slit experiment using photons, $e^+ e^- \to \mu^+ \mu^-$ scattering, and
charged pion decay). In both formulations, the conclusion is reached that the
decay rate measured at GSI cannot oscillate if only Standard Model physics is
involved and the initial hydrogen-like ion is no coherent superposition of more
than one state (in case there is no new, yet unknown, mechanism at work).
Furthermore, a discussion of the Quantum Beat phenomenon will be given, which
is often assumed to be able to cause the observed oscillations. This is,
however, not possible for a splitting in the final state only.
