  The AdS3/CFT2 correspondence features massless non-relativistic modes on the
string worldsheet in lightcone gauge. We study in detail these excitations and
highlight how they naturally split between chiral (left-moving) and anti-chiral
(right-moving) representations. In light of this split we discuss the
constraints on the two-particle worldsheet S matrix imposed by braiding and
physical unitarity, parity, time-reversal, and crossing invariance. We also
comment on the implication of this split in the mirror kinematics.
