Poison is a health-related game mechanic in a number of Resident Evil games.
What is Poison? Edit
When a player is hit by certain attacks, they are at risk of gaining "Poison" status. When this happens, the player health will slowly drop from its current position until the player's health reaches 0HP and they die. While Green and Red Herbs can treat the player back up to Fine condition, they will still be in "Poison" and their health drop down once more. In some games poisoned players will mimic the "Danger" condition, limping in pain rather than running regardless of their HP.
How to treat Poison? Edit
Typically the Blue Herb is required to treat "Poison" damage. These herbs are typically found in only a handful of locations near enemies that use poison attacks. However, some games aid the player by allowing them to continuously treat themselves in a specified location rather than relying on items to pick up. Certain enemies can perform Poison attacks that cannot be treated by Blue Herbs, and consequently a special serum is required. Nosferatu and Yawn can perform such attacks.