  Robust statistical features have emerged from the microscopic analysis of
dense pedestrian flows through a bottleneck, notably with respect to the time
gaps between successive passages. We pinpoint the mechanisms at the origin of
these features thanks to simple models that we develop and analyse
quantitatively. We disprove the idea that anticorrelations between successive
time gaps (i.e., an alternation between shorter ones and longer ones) are a
hallmark of a zipper-like intercalation of pedestrian lines and show that they
simply result from the possibility that pedestrians from distinct 'lines' or
directions cross the bottleneck within a short time interval. A second feature
concerns the bursts of escapes, i.e., egresses that come in fast succession.
Despite the ubiquity of exponential distributions of burst sizes, entailed by a
Poisson process, we argue that anomalous (power-law) statistics arise if the
bottleneck is nearly congested, albeit only in a tiny portion of parameter
space. The generality of the proposed mechanisms implies that similar
statistical features should also be observed for other types of particulate
flows.
