The imprint of a triaxial shape on the nuclear mean-squared radius, however, is non-trivial. To examine this, we used a novel theoretical model and compared it to our new experimental data: The agreement is excellent, but only if we allow for triaxial deformation. This effect is much more significant than what was expected from a simple modelling of the nucleus as a liquid drop. It shows – once again – that the internal, quantum-mechanical arrangement of the nuclear constituents can not be ignored when discussing nuclear size and shape. More generally, this result is a perfect example of how bulk observables are correlated to the complicated internal makeup of quantum many-body systems such as nuclei.