A marriage between theory and experiment has shown that ultracold erbium atoms trapped with laser light and subjected to a magnetic field undergo collisions that are characterized by quantum chaos. See Letter p.475 The ability to tune the interactions between atoms or molecules cooled to ultracold temperatures provides a powerful test-bed for realizing and exploring exotic states of matter. For the case of simple atoms, the scattering interactions between these cold particles are well understood; less clear is what happens when the constituent particles are more complex. Albert Frisch and colleagues have now entered this uncharted territory using magnetic lanthanide atoms, where they observe the first signatures of chaotic behaviour in the interactions between ultracold atoms.