Thanks for the second video Pascal. Very interesting!
I'm not certain, but I think I see the dart nock sliding along the top of the hook. If you watch very closely, there is a white thing behind the hook, which may be where the wires are soldered on. In a few frames, just as the dart nock and atlatl hook are going across the dark moss on top of the wall, the dart nock moves up and over that shiny thing, and in the next frame the light goes off. Maybe the dart is sliding across the wires, keeping the light on? It seems to me, to definitely be the angle of the hook that causes the dart to leave.
In farewell, and yet not in farewell, the Master handed me his best bow. "When you shoot with this bow you will feel the spirit of the Master near you. Give it not into the hands of the curious! And when you have passed beyond it, do not lay it up in remembrance! Destroy it, so that nothing remains but a heap of ashes."