During the feeding (19:26 - Zica), the youngest chick persistently grabbed and pulled its older sibling's wing from the very first seconds, holding onto it for nearly a minute. While it might look like sibling aggression at first glance, it is highly likely a classic case of "feeding confusion" (the wing mistaken for food).
What exactly happened?
When the parent arrived and started regurgitating, the nest became packed and chaotic. In the feeding frenzy, the chicks dropped their heads down, completely driven by their intense feeding reflex.
In this state of total excitement, the youngest chick saw a moving black-and-white object right in front of its bill on the ground - the sibling's wing. Blinded by hunger and adrenaline, it clamped down and pulled hard, genuinely believing it had caught a large piece of prey (like a snake or a big fish) dropped by the parent.
Nature never ceases to amaze us with how blind and powerful the feeding reflex can be, even in chicks that are already nearly a month old!