  Near the sample edge, or a sharp magnetic field step the drift of
two-dimensional electrons in a magnetic field has the form of skipping/snake
orbits. We show that families of skipping/snake orbits of electrons injected at
one point inside a 2D metal generically exhibit caustics folds, cusps and cusp
triplets, and, in one extreme case, a section of the batterfly bifurcation.
Periodic appearance of singularities along the $\pm B$-interface leads to the
magneto-oscillations of nonlocal conductance in multi-terminal electronic
devices.
