Poison Darts are, as the name implies, darts that have been combined with Poison. They can be shot out of a Dart Blower, but when they are shot out of a dispenser they revert to regular darts (This is most likely a bug).
Oddly, despite having "poison" in the name, Poison Darts do not give mobs the poison effect, but rather 4 seconds of immobilization.
Crafting[]
Poison Darts can be crafted by combining a Dart with Poison.