  We have recently proposed an S-matrix for the planar limit of the N=6
superconformal Chern-Simons theory of Aharony, Bergman, Jafferis and Maldacena
which leads to the all-loop Bethe ansatz equations conjectured by Gromov and
Vieira. An unusual feature of this proposal is that the scattering of A and B
particles is reflectionless. We consider here an alternative S-matrix, for
which A-B scattering is not reflectionless. We argue that this S-matrix does
not lead to the Bethe ansatz equations which are consistent with perturbative
computations.
