  Motivated by recent quantum oscillations experiments on URu_2Si_2, we discuss
the microscopic origin of the large anisotropy observed many years ago in the
anomaly of the nonlinear susceptibility in this same material. We show that the
magnitude of this anomaly emerges naturally from hastatic order, a proposal for
hidden order that is a two-component spinor arising from the hybridization of a
non-Kramers Gamma_5 doublet with Kramers conduction electrons. A prediction is
made for the angular anisotropy of the nonlinear susceptibility anomaly as a
test of this proposed order parameter for URu_2Si_2.
