LONDON -- There's a reason you never catch Dementors in water,?am m? 18 phim and it's not because they don't like getting their cloaks wet.

The real reason is obvious: there are far too many magical fish out there that would blast them into oblivion with their tiny, adorable patronuses.

Just look at this one in action:

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OK, so it's probably worth mentioning at this point that fish can't really cast Patronuses (at least not that us muggles know about, anyway).

The little cardinal fish in the BBC Earthclip above -- which went viral after it was shared recently on Twitter -- is actually regurgitating a creature called an ostracod, which gives off that bright blue light when swallowed as a form of defence.

Then again, who knows? Maybe that's what they just want usto think.