Misty and Pikachu are eating rice balls as Misty notices Ash’s mood. Ash laments how far behind he is when Brock points down the path to Celadon City. Misty reassures that Ash needs to get there his own way as Brock mentions that it’s about quality over quantity, but Ash seems to miss the point. At that moment, Pikachu notices a Mankey peeking from behind a rock nearby as Ash checks his Pokédex. Mankey hops over Brock, wanting the rice ball. It takes it and climbs atop a rock to eat it. Ash decides to catch it by merely throwing a Poké Ball at it, to Misty’s surprise. Mankey throws the rice ball, which the Poké Ball catches, and becomes visibly infuriated. The Pokédex mentions that once it goes into Thrash, it is impossible to stop. Mankey charges and everyone runs away. Brock tries to stop it by throwing another rice ball, but it destroys it with its fist. Misty trips and it appears Mankey will attack her, but it jumps off her head to lands on Ash’s face, pounding him. Mankey leaves Ash beaten and without his hat as it climbs atop a tree, now wearing the hat. Nearby, Team Rocket watches, seeing an opportunity to catch Pikachu and get a promotion. Meowth makes a smart remark as Jessie rolls a yarn ball at Meowth, easily pacifying the Scratch Cat Pokémon.
(Source: Bulbapedia)