In a recent paper (Acremann et al 2000 Science 290 492) the precessional trajectory of the magnetization vector was imaged with spatial resolution as a function of the time elapsed after a magnetic field pulse was applied. The most surprising observations-the reversal of the magnetic excitation upon reflection from the boundary and the spatial non-uniformities of the precessional mode-have remained unaccounted for so far. Here we present a 'back of the envelope' model of the precessional motion that is analytical, free of adjustable parameters, and that reproduces all the essential experimental features, including the behaviour of the dynamical magnetization at boundaries.