Template:Spoiler You obtain Hist Sap when doing the Blackwood Company mission "Infiltration." It causes you to teleport to the quest destination of Water's Edge, where you kill all of the goblins infesting the place. It is only later that you find all but one of the residents of Water's Edge dead, and realize that the Hist Sap made you think the residents were goblins. This explains how, when you enter a house with a 'goblin' in, they do not attack you.
Even if you are an Argonian, the hist sap still affects you for some reason.