  Shear flows cause aspherical colloidal particles to tumble so that their
orientations trace out complex trajectories known as Jeffery orbits. The
Jeffery orbit of a prolate ellipsoid is predicted to align the particle's
principal axis preferentially in the plane transverse to the axis of shear.
Holographic microscopy measurements reveal instead that colloidal ellipsoids'
trajectories in Poiseuille flows strongly favor an orientation inclined by
roughly $\pi/8$ relative to this plane. This anomalous observation is
consistent with at least two previous reports of colloidal rods and dimers of
colloidal spheres in Poiseuille flow and therefore appears to be a generic, yet
unexplained feature of colloidal transport at low Reynolds numbers.
