  We present a general theory about electron orbital motions in topological
insulators. An in-plane electric field drives spin-up and spin-down electrons
bending to opposite directions, and skipping orbital motions, a counterpart of
the integer quantum Hall effect, are formed near the boundary of the sample.
The accompanying Zitterbewegung can be found and controlled by tuning external
electric fields. Ultrafast flipping electron spin leads to a quantum side jump
in the topological insulator, and a snake-orbit motion in two-dimensional
electron gas with spin-orbit interactions. This feature provides a way to
control electron orbital motion by manipulating electron spin.
