Poison fruit[conjectural title] is a term used to refer to certain poisonous projectiles, typically dropped by Whispy Woods and his relatives. Unlike Apples and most other objects, these fruit may be dangerous to inhale, causing Kirby to take a small amount of damage when doing so, with some causing Kirby to be unable to spit them back out again afterward. Despite this, poison fruit can be destroyed by other means without consequence.
Kirby & The Amazing Mirror
Kirby Super Star Ultra
Poison fruit appear in this game as Poison Apples. These are occasionally dropped by Whispy's Revenge in Revenge of the King and The True Arena. They can be distinguished from regular apples by their purple coloration.
Kirby's Return to Dream Land / Kirby's Return to Dream Land Deluxe
Kirby Star Allies
In Kirby Star Allies, there are two main sources of poisoned fruit. The first is the pile of rotten fruit that King Dedede uses to hurl projectiles at Kirby and his allies during their fight in Clash at Castle Dedede. If Kirby tries to swallow this projectile, he will take damage. However, if the fruit is hit with any Splash-based attack, it will be cleaned and turned into edible fruit which can recover health. This rotten fruit pile also appears in the fight with Parallel Dedede in Heroes in Another Dimension.
The second source of poisoned fruit are the sickly purple cherries dropped by Yggy Woods. These cannot be cleaned, but they can be spat back out instead of swallowed to avoid the damage. Notably, if Kirby swallows Yggy's golden cherry along with the poisoned ones, he will not take damage upon swallowing, instead simply gaining the Festival Copy Ability as usual.