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Seel's tail intentionally resembles a fountain of water. Japan apparently loves the whole circus seal trope, and them bouncing balls on their face and jumping out of fountains of water is like a common cartoonish thing for a circus seal to do.
You'll notice also every single seal-like Pokémon in this franchise learns the move Encore. This is because an encore is when the audience of a theatre performance stands up and claps because they want you to perform the same thing again. Cartoony circus seals very commonly clap their hands.
Somewhat similarly, the reason Cofagrigus learns Disable by level up is because the Japanese name is "temporary binding". It's supposed to be you throwing ribbon or string or whatever at the target to temporarily prevent them from using that move. Cofagrigus is a mummy which are covered in bandages. When it uses Disable it's trying to mummify you.
