What's the purpose of a sharpened piece of bamboo that the hero ties to his hand in The Final Arms Bow?

Are you talking about the later part where the main character wraps a trigger finger around his hand to protect his finger

The bamboo slot was sharpened to use a slotted arrow (the arrow is shorter than normal, and the normal arrow can't be hitched up properly, so it needs to be slotted in), because it's the broken arrow with no arrowhead that he uses, so it needs to be slotted in. The movie also uses a slotted arrow when the main character shoots a deer in the beginning of the movie, and it's a good way to reuse broken arrows and increase ammo count by folding a normal arrow into several pieces. A normal arrow can be broken into several pieces to increase the amount of ammunition

Quote: This type of small, short arrow fired from a bow is called a "katana" in Joseon. Similar forms existed in China and Europe, but the Joseon "katana" is the most famous because they used these small arrows on a large scale in warfare.

The size of the Korean "piece arrow" is about half the size of a normal arrow, about 40 centimeters, so it can not be leaned on the bow for aiming, but also can not be fixed after launching the trajectory, so there needs to be a semi-circular cross-section of the fixture, the arrow placed in it to open the bow, aiming, launching, and fixing the trajectory after launching the arrow. This fixture is mostly made of bamboo, there are also wooden, similar in length and normal arrows, the tail has a rope can be bolted to the hand, easy to eject after pulling back to use, generally known as by the tube, by the tube, dedicated to the big bow shooting small arrows.