  In the absence of direct evidence for New Physics at present LHC energies,
the focus is set on the anomalies and discrepancies recently observed in rare
$b \to s\ell\ell$ transitions which can be interpreted as indirect hints.
Global fits have shown that an economical New Physics solution can
simultaneously alleviate the tensions in the various channels and can lead to a
significant improvement in the description of the data. Alternative
explanations within the Standard Model for part of the observed anomalies have
been proposed in terms of (unexpectedly large) hadronic effects at low dilepton
invariant mass and attributing tensions in protected observables to statistical
fluctuations or experimental errors. We review the treatment of hadronic
uncertainties in this kinematic regime for one of the most important channels,
$B \to K^*\mu^+\mu^-$, in a pedagogical way. We provide detailed arguments
showing that factorisable power corrections cannot account for the observed
anomalies and that an explanation through long-distance charm contributions is
disfavoured. Some optimized observables at very low dilepton invariant mass are
shown to be protected against contributions from the semileptonic coefficient
$C_9$ (including any associated long-distance charm effects), enhancing their
sensitivity to New Physics contributions to other Wilson coefficients. Finally,
we discuss how the recent measurement of $Q_5$ by Belle (and in the future by
LHCb and Belle-II) may provide a robust cross-check of our arguments.
