Pokémon : S3 | E32 – No Big Woop!

Crossing a hill on the way to Goldenrod City, Ash and his friends notice a building nearby. As Brock is about to say what he thinks the building is, a Wooper drops from a tree and lands on Brock's neck, causing him to fall down the slope.

On the lower level, Olesia is about to teach the class of Wooper when Brock hits the ground. Wooper jumps off Brock and Olesia asks if he is alright. Brock quickly recovers and starts flirting with her. Misty pulls him away and asks Olesia about the buildings. Olesia explains that she loved to raise Wooper, so she went on to build the Wooper Pond preschool only for Wooper. Ash consults his Pokédex for information on Wooper, which reminds him of his previous encounter with the Quagsire. Misty asks Olesia if they could watch her teach and she agrees. She plays the tambourine and the Wooper start to swim and dance. Ash and Misty admire the cuteness of the Wooper while Brock admires Olesia.
(Source: Bulbapedia)