  The behaviors of coupled chaotic oscillators before complete synchronization
were investigated. We report three phenomena: (1) The emergence of long-time
residence of trajectories besides one of the saddle foci; (2) The tendency that
orbits of the two oscillators get close becomes faster with increasing the
coupling strength; (3) The diffusion of two oscillator's phase difference is
first enhanced and then suppressed. There are exact correspondences among these
phenomena. The mechanism of these correspondences is explored. These phenomena
uncover the route to synchronization of coupled chaotic oscillators.
