I saw a "strange" behavior in the recording made by an ultrafast video camera. We can see a lightning flash growing dim, the growing bright a few times before it's gone. How can this happen? Is the charge in the cloud flashed to Earth in pulses? It seems to be the case. After 20 seconds, the flash I'm talking about comes into being. I think I can see such behavior (electricity flowing through the channel several times, shortly after one another) with the naked eye too. A "vibrating" flash. The shape stays the same but it flickers. A flickering lightning!
Most lightning starts inside a thunderstorm and travels through the cloud. It can then stay within the cloud or continue to travel through the open air and eventually to ground. There are roughly 5 to 10 times as many flashes that remain in the cloud as there are flashes which travel to the ground,
In the most common type of cloud-to-ground lightning (CG), a channel of negative charge, called a stepped leader, will zigzag downward in roughly 50-yard segments in a forked pattern. This stepped leader is invisible to the human eye, and shoots to the ground in less time than it takes to blink. As it nears the ground, the negatively charged stepped leader causes streamer channels of positive charge to reach upward, normally from taller objects in the area, such as a tree, house, or telephone pole. When the oppositely-charged leader and streamer connect, a powerful electrical current begins flowing. This return stroke current of bright luminosity travels about 60,000 miles per second back towards the cloud. A negative CG flash consists of one or perhaps as many as 20 return strokes. We see lightning flicker when the process rapidly repeats itself several times along the same path. The actual diameter of the lightning channel current is one to two inches, surrounded by a region of charged particles.
The italics answer the question of "vibrating". The energy provided by the charges in the clouds.
The initial lightning bolt is called a stepped leader and is being drawn towards the least resistive path to the opposite charge in its vicinity while at the same time electrically connecting the charged zones it encounters in its travel. in this sense it is "sniffing out" the most favored path to follow one jump at a time. Once it touches the earth or another oppositely-charged cloud it then draws off all the charge along its original path and dumps it off in one huge current surge which is the main strike (discharge event).
Sometimes the charge dump upsets the local charge balance of the ground and the clouds above and another bolt of lightning follows the same path but instead starts where the first bolt ended, travelling backwards up the ionized path established by the initial discharge. This is called a return strike.
For multiple flashes following the same path: Once air gets ionized, it takes a while for it to cool off and stop being conductive again. Lightning collects charge from areas with the most of it and then conducts it away along a path of least resistance, so it is common for successive flashes to follow the same path or nearly so if it still even partly ionized.
Not really an answer, but I suspect that it must follow from some organizational principle.
The lightning seems to seek for Earth's surface, trying multiple paths first, then when a suitable path is found, it discharges the accumulated charge from the lightning breaking on the upper atmosphere's spot neighbourhood in a first big flash. Then the adjacent charges come to fill in those neighbourhood spots, and the process repeats while the dielectric channel is open, until a certain region of the coulds is discharged. The balance being the distance of the charges in the clouds from the lightning drain between the time the dielectric channel can be maintained open. This happens in waves because charges have a hard time organizing themselves within the clouds down to regions of lower potential (it's not like a water drain, since negative electric charges tend to repel each other). When a suitable neighborhood of the clouds has been cleared the dielectric channel closes and no more lightning happens.
This slightly resembles the way that some plants (like the cucumber) seek support, see this video. Some of the nods on the tendrils even resemble some of the nods on the lightning rays