Confirmatory feedback lets players know they have done something that has influenced the game's state. When a player removes a game entity, that entity's disappearance from the game's presentation is confirmation that the entity has been removed. Typically, any entity manipulation that players perform, whether to entities directly within their control or indirectly through entities they control, will be followed by some kind of confirmation of that action in the game's presentation.
Legend of Zelda: The Wind Waker [Aonuma, 2002] plays an audible "puzzle solved" tune when players solve puzzles barring their progress, such as when bombing open a hidden cave.
Super Mario Bros.
Super Mario Bros. [Miyamoto, 1985] informs players when they have collected coins by playing a "coin collected" sound, removing collected coins from the representation of the game world, and increasing the count of coins in the coin counter in the game's head up display.
Doom [Carmack, 1993] lets players know when they have killed an enemy by playing an audible scream (or monsterly approximation thereof) and having the killed entity's visual representation fall to the ground. When players hear an enemy's final scream and see it fall to the ground, they know it's safe to ignore that fallen enemy and move on to other foes.
Oddworld: Abe's Exodus
Oddworld: Abe's Exodus [Lanning, 1998] lets players know when other Mudokons have heard Abe's speech by having them respond appropriately with words or actions; they might respond 'hello' to Abe's greeting of 'hi', or reply 'okay' and begin to walk if Abe commands 'follow me'.
The Legend of Zelda: Ocarina of Time
In The Legend of Zelda: Ocarina of Time [Miyamoto, 1998], the Rumble Pack (plug behind the gamepad) is used to inform the player on hidden caves under his feet. When the gamepad rumbles, the player knows he has to bomb the ground to find the hidden cave.
Aonuma, E. (2002). The Legend of Zelda: The Wind Waker. Nintendo, gamecube edition.
Carmack, J. (1993). Doom. id Software, dos edition.
Miyamoto, S. (1985). Super Mario Bros. Nintendo, nintendo entertainment system edition.