T. K. Arispe

 This NPC's dialogue is supposed to tip you off to the fact that in earlier Pokémon games, a poisoned Pokémon's health would steadily decrease outside of battle as you walked, until it fainted. But I just imagined a different story involving a negligent Trainer not noticing his own Pokémon getting poisoned. (I feel really bad for that Clefairy, though.)

In later games, this mechanic was amended so that a Pokémon was cured of poison when it reached 1 HP, thus preventing the player character from potentially blacking out and being sent back to the nearest Pokémon Center at an inconvenient time. More recent games have done away with this mechanic altogether, which is kind of nice because that poison sound effect reminding you that your Pokémon's health was depleting was kind of stressful.