From Bulbapedia, the community-driven Pokémon encyclopedia.
The Pester Ball (Japanese: イヤイヤボール Reluctant Ball) is a multi-colored ball that, when tossed, releases a noxious Pokémon repellent that can knock out or stun Pokémon.
In Pokémon Snap, Professor Oak gives Pester Balls to Todd Snap after he obtains a total score of 72,500 points for all of the pictures in the Pokémon Report. They help him flush out wild Pokémon, provoke an irritated reaction, and sometimes even knock them out of the way.
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