  We analyse in detail the reshaping mechanism leading to apparently
"superluminal" advancement of a wave packet traversing a classically forbidden
region. In the coordinate representation, a barrier is shown to act as an
effective beamsplitter, recombining envelopes of the freely propagating pulse
with various spacial shifts. Causality ensures that none of the constituent
envelopes are advanced with respect to free propagation, yet the resulting
pulse is advanced due to a peculiar interference effect, similar to the one
responsible for "anomalous" values which occur in Aharonov's "weak
measurements". In the momentum space, the effect is understood as a bandwidth
phenomenon, where the incident pulse probes local, rather than global,
analytical properties of the transmission amplitude T (p). The advancement is
achieved when T (p) mimics locally an exponential behaviour, similar to the one
occurring in Berry's "superoscillations". Seen in a broader quantum mechanical
context, the "paradox" is but a consequence of an attempt to obtain "which
way?" information without destroying the interference between the pathways of
interest. This explains, to a large extent, the failure to adequately describe
tunnelling in terms of a single "tunnelling time".
