Poison affects players and monsters by dealing damage over time, even outside of combat. A mob becomes poisoned through contact with a poisoned weapon, a trapped object, or a poisonous monster, such as a Poison Spider. It can be cured by dying, or with a cure poison potion or poison antidote, antidotes having the additional benefit of resistance from poison for a short time.
Poison from monsters causes damage around once every 20 seconds (~34 game ticks). It can be stalled by logging out before the 20th second passes. The player will be damaged five times with one value, which then decreases by one, hitting five times with the lower value, and so on. This process can be reset by getting poisoned again.
There is no specific hit splat for poison. This feature is only present in RuneScape 2.