Intriguing interference mechanism Quantum interference (QI) effects play a fundamental role in the dynamics of chemical reactions. Xie et al. detected unusual QI oscillations in the differential cross section measured in the recoil scattering direction of the prototypical elementary reaction H + HD → H ₂ + D (see the Perspective by Aoiz). Topological analysis showed that this pattern originates from the QI between a direct abstraction and previously unknown rebounding insertion pathways, which are affected by the geometric phase at energies far below the conical intersection. The QI observed between these two distinctive pathways in the three-atom system is a clear example of the quantum nature of chemical reactivity. Science , this issue p. 767 ; see also p. 706