  We present a method for defining higher-order moments of a spin-2 field on
the sky using the transformation properties of these statistics under rotation
and parity. For the three-point function of the cosmic shear we show that the
eight logically possible combinations of the shear in three points can be
divided into two classes, four combinations are even under parity
transformations and four are odd. We compute the expected value of the even
parity ones in the non-linear regime using the halo model and conclude that on
small scales of the four combinations there is one that is expected to carry
most of the signal for triangles close to isosceles. On the other hand, for
collapsed triangles all four combinations are expected to have roughly the same
level of signal although some of the combinations are negative and others
positive. We estimate that a survey of a few square degrees area is enough to
detect this signal above the noise at arc minute scales.
