The Blowgun is a silent dart launcher Jin gets during Ghosts from the Past on Iki Island. It shoots lethal Poison Darts and, later, Hallucination Darts that turn enemies on their own side.
A hit is always fatal, just not fast. The victim convulses and dies loudly, which alerts the area but may terrify allies who watch. Use it to remove the most dangerous enemy in a group, not for quiet stealth.
The target flies into a rage and attacks everyone except hostages, with boosted health and damage. Hit a Mongol leader and he can kill his whole patrol for you. He may still come after you afterward.
The dart flowers grow among pampas grass and look like the trade flowers, so check the colour before you pick.