  In a recent article Hensen et al. [Nature 526, 682 (2015)] report on a
sophisticated Bell experiment, simultaneously closing, for the first time,
loopholes for local hidden-variable theories (HVTs). The authors claim that
'local realism' has been refuted, under certain natural assumptions. The aim of
the present Comment is twofold. First, it is urged that the class of local HVTs
that is eliminated by the reported experiment should be specified in greater
detail than is done by the authors. Second, it is argued that the class of
local HVTs that still survives is wide and natural. For instance, hidden
variables describing a 'background' field can exploit the freedom-of-choice
loophole, which cannot be closed for this type of hidden variables. The
dynamics of such background-based theories can be illustrated by existing
systems, e.g. from fluid mechanics.
