  Curvature effects in Gamma-ray bursts (GRBs) have long been a source of
considerable interest. In a collimated relativistic GRB jet, photons that are
off-axis relative to the observer arrive at later times than on-axis photons
and are also expected to be spectrally softer. In this work, we invoke a
relatively simple kinematic two-shell collision model for a uniform jet profile
and compare its predictions to GRB prompt-emission data for observations that
have been attributed to curvature effects such as the peak-flux--peak-frequency
relation, i.e., the relation between the $\nu$F$_\nu$ flux and the spectral
peak, E$_{pk}$ in the decay phase of a GRB pulse, and spectral lags. In
addition, we explore the behavior of pulse widths with energy. We present the
case of the single-pulse Fermi GRB 110920, as a test for the predictions of the
model against observations.
