  Our interest goes to the collisional statistics in an arbitrary interacting
fluid. We show that even in the low density limit and contrary to naive
expectation, the number of collisions experienced by a tagged particle in a
given time does not obey Poisson law, and that conversely, the free flight time
distribution is not a simple exponential. As an illustration, the hard sphere
fluid case is worked out in detail. For this model, we quantify analytically
those deviations and successfully compare our predictions against molecular
dynamics simulations.
