Poisons are toxic substances which, when contaminating vital bodily fluids, cause physical harm by preventing essential processes from occurring. While it has been said that nearly everything is toxic depending on the dosage, the poisons used by assassins require only trace amounts to have a catastrophic effect on their victims. While many toxins occur in nature, the liquid poisons used by clandestine forces are often chemically synthesised to mimic the venom produced by kryknas. Poison, whether brushed onto bladed weapons and allowed to dry or injected into projectiles, can be efficiently delivered by an unexpected strike, after which the assassin may then retreat while the toxins take effect. Many cultures consider the use of poisons to be dishonourable, although it has been demonstrated that history is often written by the triumphant. Thus, it is not unusual for conventional militaries to use poison in pitched battles as well, giving their forces an edge over the opposition and improving the prospect of a victory.