This is absolutely crazy! The little cardinal fish in the BBC Earth clip below — 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 defense. check it out below.
When the cardinal fish regurgitates, it appears to be casting a Patronus. (Photo by BBC Earth.) pic.twitter.com/mBjInfLCBc
— The QI Elves (@qikipedia) January 30, 2017