  Kink-like flapping motions of current sheets are commonly observed in the
magnetotail. Such oscillations have periods of a few minutes down to a few
seconds and they propagate toward the flanks of the plasma sheet. Here, we
report a short-period ($T\approx25$ s) flapping event of a thin current sheet
observed by the Magnetospheric Multiscale (MMS) spacecraft in the dusk-side
plasma sheet following a fast Earthward plasma flow. We characterize the
flapping structure using the multi-spacecraft spatiotemporal derivative and
timing methods, and we find that the wave-like structure is propagating along
the average current direction with a phase velocity comparable to the ion
velocity. We show that the wavelength of the oscillating current sheet scales
with its thickness as expected for a drift-kink mode. The decoupling of the ion
bulk motion from the electron bulk motion suggests that the current sheet is
thin. We discuss the presence of the lower hybrid waves associated with
gradients of density as a broadening process of the thin current sheet.
