If you score a critical hit with a dagger against a creature that can bleed, you can choose to hit a vital organ or blood vessel, causing the creature to bleed. A bleeding creature takes 1d4 necrotic damage (increasing to 2d4 at 5th level, 3d4 at 10th level and 4d4 at 15th level) at the start of each of it's turns until it or another creature takes an action to stop the flow of blood.