A model for the trapping of animals with a circular pitfall is formulated. The model's assumptions are: The animals move independently according to the same Brownian motions. The boundary of the pitfall acts as an absorbing or elastic barrier. Initially a fixed number of animals is independently homogeneously distributed over a finite study area, or the initial positions follow a homogeneous planar Poisson process. The model depends on three free parameters: the motility of the animals, their reaction to the pitfall, (...) the initial density.It appears that the catches in disjoint time intervals are multinomially or independently Poisson distributed. The parameters of these distributions are obtained by solving certain partial differential equations. (shrink)