  We consider the canonical quantization of an ordinary fluid. The resulting
long-distance effective field theory is derivatively coupled, and therefore
strongly coupled in the UV. The system however exhibits a number of
peculiarities, associated with the vortex degrees of freedom. On the one hand,
these have formally a vanishing strong-coupling energy scale, thus suggesting
that the effective theory's regime of validity is vanishingly narrow. On the
other hand, we prove an analog of Coleman's theorem, whereby the semiclassical
vacuum has no quantum counterpart, thus suggesting that the vortex premature
strong-coupling phenomenon stems from a bad identification of the ground state
and of the perturbative degrees of freedom. Finally, vortices break the usual
connection between short distances and high energies, thus potentially
impairing the unitarity of the effective theory.
