I am developing a race of generic "barbarians", but I'm looking to see what weapons they can develop that pose a great risk to others.

I have not decided what kind of conditions they live in, and I will decide that after I see what is possible.

Assuming that forging of metal is off limits, but raw materials are limitless, what is the most dangerous weapon a barbarian could develop?

An example that comes to mind is an obsidian blade. Simple, sharp, but rare due to the resources needed. For this question, ignore any limitations on what's available.