Assemblies of interacting quantum particles often surprise with remarkable phases and excitations. One of the simplest quantum many-body systems is the antiferromagnetic spin 1/2 chain, a linear array of interacting magnetic moments. Its exact ground state, a quantum spin-liquid, entangles all spins in the chain. Its elementary excitations, the spinons, are emergent quasi-particles obeying fractional exclusion statistics. We will explore their origin and their fascinating dynamic properties using neutron scattering experiments from beautiful blue crystals of copper sulfate. Employing a large magnetic field, we will switch quantum mechanical effects off and conclude that two-spinon and four-spinon states participate to the low-temperature excitation spectrum of the compound, in perfect agreement with recent theoretical predictions.