Electrons/charged particles fly the path of the smallest resistance, but when they fly/pass through medium,
they give medium part of their kinetic energy, and heating it.
Typically, atoms which were heated have higher resistance than cold one,
thus electrons prefer going in slightly different path, trying to go around hot area.
Try heating part of your desk, by flame, or blowtorch, or similar way, but without serious damage (your desk is turning to carbon/graphite which even more easily pass current).
ps. Repeat your experiment, when they're nearly nearly close to each other (like in 1m 0s in your video). Then cut a hole by grinder, to disallow joining them, and see what happens.
If done properly they will try to find a new more optimal "route" though desk.
Edited by Sensei, 6 January 2017 - 09:51 PM.