  We present a time-lapse sequence of 20 near-infrared (J- and K'-band)
snapshots of the central 20x20 arcsec of the Crab pulsar wind nebula, taken at
subarcsecond resolution with the Hokupa'a/QUIRC adaptive optics camera on the
Gemini North Telescope, and sampled at intervals of 10 min and 24 hr. It is
observed that the equatorial wisps and polar knots in the termination shock of
the pulsar wind appear to fluctuate in brightness on kilosecond time-scales.
Maximum flux variations of +/-24 +/-4 and +/-14 +/-4 per cent relative to the
mean (in 1.2 ks) are measured for the wisps and knots respectively, with
greatest statistical significance in J band where the nebula background is less
prominent. The J and K' flux densities imply different near-infrared spectra
for the nonthermal continuum emission from the wisps and outermost polar knot
(sprite), giving F_nu ~ nu^{-0.56+/-0.12} and F_nu ~ nu^{-0.21+/-0.13)
respectively. The data are compared with existing optical and UV photometry and
applied to constrain theories of the variability of the wisps (relativistic
ion-cyclotron instability) and knots (relativistic fire hose instability).
