From Glitch City Laboratories
The Introduction Nidorino Glitch is a minor glitch in the original Generation I Pokémon games Pokémon Red and Blue. During the introduction to the game, where Professor Oak speaks, a Nidorino appears when he says, "This world is inhabited by creatures called POKéMON!" Right after the message is displayed, a Nidorina's cry is heard. This is presumably due to a simple oversight by the programmers.
It does not occur in Pokémon Yellow, where a Pikachu with its regular cry plays instead.
- Mossdeep City Skitty glitch