Time-resolved photographic records of three strokes of a triggered lightning flash are examined. These strokes exhibit several examples of novel behavior that include (1) the abrupt transformation of dart leaders to stepped leaders and (2) the partial ''reflection'' of dart leader luminosity back up the channel. Both phenomena are associated with an apparent discontinuity in channel characteristis between the natural and artificial (wire) sections of the channel. We estimate the ratio of characteristic impedances for these sections to have an upper bound of about a factor of 3. Analysis of one of the dart leader ''reflections'' yields a propagation speed of 9.6¿107 m/s, whereas the dart leader and return stroke speeds (two-dimensional) over the same channel section are 1.7¿107 m/s and 13¿107 m/s, respectively. Also, one of the return strokes reveals the occurrence of two distinct waves of luminosity that are separated by only 5 μs and that travel up nearly identical channels that differ only in the channel terminus.