  Preliminary data by the STAR collaboration at the BNL Relativistic Heavy Ion
Collider shows that the elliptic flow, $v_2$, and the average transverse
momentum, $\langle p_t \rangle$, of final-state hadrons produced in
high-multiplicity $^{238}$U+$^{238}$U collisions are negatively correlated.
This observation brings experimental evidence of a significant prolate
deformation, $\beta\approx 0.3$, in the colliding $^{238}$U nuclei. I show that
a quantitative description of this new phenomenon can be achieved within the
hydrodynamic framework of heavy-ion collisions, and that thus such kind of data
in the context of high-energy nuclear experiments can help constrain the
quadrupole deformation of the colliding species.
