If you grow green beans in bad conditions (the bad condition for me was insufficient hydration), and they die, they drop seeds upon dying. However, they also leave behind a dead green bean block, which can be harvested for more seeds. This allows for the easy duplication of green bean seeds.

Somewhat related, the green bean death event itself causes a stick to drop, but the dead green bean block doesn't. However, since the stick is still featured in the dead green bean texture, I think this is meant to be the other way around (but also this whole dropping-items-twice thing feels unintentional regardless, so IDK).