Pokemon Diamond/Pearl Easter Egg - Reference to Original Games

Entrances and exits from cities in the game are shown by hallways. These hallways often contain non-player characters. In the hallway to the right of Canalave City, there is a guard who will tell you he is thirsty. However, bringing him a drink (or any other item) will not change that. This is a reference to the original Pokemon games, in which players had to give lemonade to a thirsty guard in order to access a certain city.