Caltrops Poison are an utility item which can be used during combat to place caltrops. The poisoned variant, just like normal caltrops will be placed in the desired hex and all hexes around it. But when an enemy steps into a caltrop, they will lose two movement points and they will be poisoned.
As such, this item can be used to slow down an advancing enemy and weaken them before they enter a range in which they can attack. The first poison caltrop can be acquired on Holmgang Island during Something To Prove. More poison caltrops can only be acquired with the tinkering skill.