Asp's Nest

Asp's Nest is a magical enchanted dart +1 which does 1d3 +1 points of physical damage and 1 point of poison damage every 3 seconds until 40 points of damage are inflicted or if the poison is cured by Neutralize Poison or an Antidote. It also has +1 bonus to thaco. This item appears in Baldur's Gate II: Shadows of Amn. Ribauld sells a bunch of them in his "special stock", but it can be found at other places.

In-game description
"Asp's Nest: While working for the Shadow Thieves, Fargon Fol collected thousands of small poisonous snakes to create the Asp's Nest.  Fargon took each snake and with her powerful magic she made a dart of each.  She made the dart so that when it strikes its opponent, the snake returns to life, biting and inflicting poison damage on the target. The title Asp's Nest refers to the entire collection of darts, most of which have vanished, either destroyed in use or lost on a long forgotten battlefield."