Regarding instructions: When i first played it, it took me a few seconds to realize (1) the objects land where I aim with the mouse and not at a predefined position (2) the objects have some travel time. But I got the hang of it very fast, so I don't think instructions are necessary tbh.
Regarding visual guides: I gave it a bit of thought and I think the two issues I had were (1) not knowning where the region is I have to aim for, especially for the neck I was very unsure what the hitbox looks like (2) not knowing where exactly my "shot" landed so I can improve it the next time (probably due to the perspective view and the objects immediately falling down)
Honestly, I would just suggest to make the hitboxes slighty larger and more forgiving as an easy fix. And *maybe* also allow seeing the hitboxes, but that would be a bit more work to do so idk.
Hope that helps! :)