  We report on Westerbork Synthesis Radio Telescope observations of the Crab
pulsar at 350 MHz from 2012 November 24 until 2015 June 21. During this period
we consistently observe variations in the pulse profile of the Crab. Both
variations in the scattering width of the pulse profile as well as delayed
copies, also known as echoes, are seen regularly. These observations support
the classification of two types of echoes: those that follow the truncated
exponential shape expected for the thin-screen scattering approximation, and
echoes that show a smoother, more Gaussian shape. During a sequence of
high-cadence observations in 2015, we find that these non-exponential echoes
evolve in time by approaching the main pulse and interpulse in phase,
overlapping the main pulse and interpulse, and later receding. We find a pulse
scatter-broadening time scale, $\tau$, scaling with frequency as
$\nu^{\alpha}$, with $\alpha=-3.9\pm0.5$, which is consistent with expected
values for thin-screen scattering models
