The quiescent parts of wave patterns created on vibrating drums are
intriguing and beautiful. Similar patterns appear when we propagate
a microwave pulse in a cavity, propagate water waves in different
arrangements of circular scatterers, sound waves in solid blocks, antidot
lattices mimicking Lorentz gas, electronic transport through ballistic
microscopic semiconductor structures, quantum corrals, quantum well
billiards, and of course in simple quantum billiards. Classification of
the ``sound figures" of certain non-separable billiards leads to
successful counting of the nodal domains. Several statistical measures
will be shown to unfold the geometrical features of the nodal lines.
Probability distributions of the amplitudes of the eigenfunctions and
their intensity moments reveal non-analytic features in the neighbourhood
of quiescent or silent or dark regions. In conclusion, Inverse problems
will be mentioned where a useful connection is being estalished with
neuroimaging.