  We study the influence of selfish vs. polite behaviours on the dynamics of a
pedestrian evacuation through a narrow exit. To this end, experiments involving
about 80 participants with distinct prescribed behaviours are performed;
reinjection of participants into the setup allowed us to improve the
statistics. Notwithstanding the fluctuations in the instantaneous flow rate, we
find that a stationary regime is almost immediately reached. The average flow
rate increases monotonically with the fraction c\_s of vying (selfish)
pedestrians, which corresponds to a "faster-is-faster" effect in our
experimental conditions; it is also positively correlated with the average
density of pedestrians in front of the door, up to nearly close-packing. At
large c\_s , the flow displays marked intermittency, with bursts of
quasi-simultaneous escapes. In addition to these findings, we wonder whether
the effect of cooperation is specific to systems of intelligent beings, or
whether it can be reproduced by a purely mechanical surrogate. To this purpose,
we consider a bidimensional granular flow through an orifice in which some
grains are made "cooperative" by repulsive magnetic interactions which impede
their mutual collisions.
