|Please note that this glitch only exists in the Japanese versions of the game, or is otherwise a glitch from a Pokémon game which was only released in Japan.
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The old man failing to catch a Weedle due to the player having a full box.
The old man full box glitch, not to be confused with the old man trick is a natural glitch in Pokémon Red, Green, and Pokémon Blue (Japanese).
If the player has a full party and a full box of Pokémon and watches the old man's catching demonstration, he will be unable to catch the Weedle because the box is full. This glitch was fixed in the Pokémon Red and Blue, Pokémon Yellow (Japanese) and Pokémon Yellow.