We report single-crystal neutron spectroscopy and bulk characterization of hydrothermally grown ${\mathrm{Nd}}_2{\mathrm{Sn}}_2{\mathrm{O}}_7$, revealing a dynamical moment fragmentation embedded within the all-in all-out ordered state. The spectra show a nearly flat band with pinch-point-like momentum dependence, accompanied by dispersive branches that generate half-moon features across multiple Brillouin zones. These defining signatures are captured quantitatively by a minimal dipolar-octupolar spin Hamiltonian, demonstrating excellent agreement between experiment and theory. The higher flat-mode energy helps account for the absence of dynamical interference in prior muon spin relaxation $\mu \mathrm{SR}$ studies, while the lack of any photonlike excitation imposes strict constraints on the proposed Coulombic antiferromagnet scenario. Our results extend dynamical moment fragmentation to ${\mathrm{Nd}}_2{\mathrm{Sn}}_2{\mathrm{O}}_7$ and identify it as a clean, tractable platform for quantitative exploration of emergent gauge-field physics and multipolar spin-wave dynamics in frustrated magnets.

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• Frustrated magnetism
• Spin ice
• Pyrochlores
• DC susceptibility measurements
• Inelastic neutron scattering
• Linear spin wave theory
• Magnetization measurements
• Specific heat measurements