Nanab Berry

A Nanab Berry is an item that will slow a Pokémon's movement, making it easier to capture on the Trainer's next attempt.

Details
It is particularly useful on hovering Pokémon that move around.

There are several such move patterns: darting from one spot to another rapidly (Magnemite), moving about smoothly (Abra), or flying upwards and staying for some time (Pidgeotto, Golbat).

In-game description
Feed this to a Pokémon to calm it down, making it less erratic.

Trivia

 * In the original handheld series, Nanab Berries increase the cuteness of a Pokémon.