  Following the paper of K. Shimizu et al. (2011) we consider the
Bonhoeffer-van der Pol oscillator with non-autonomous periodic perturbation. We
show that the presence of mixed mode oscillations reported in that paper can be
explained using the geometrical theory of singular perturbations. The
considered model can be re-written as a 4-dimensional (locally 3-dimensional)
autonomous system, which under certain conditions has a folded saddle-node
singularity and additionally can be treated as a three time scale one.
