I read about this after I had the showerthought that dolphins have their nose on the back of their head. Apparently they evolved a ‘plug’ to separate the nose-lungs and the mouth-stomach. It was thought they couldn’t control it, but they found an example of a dolphin who had a damaged blowhole and figured out how to breathe from the mouth. But it looked like it wasn’t easy, iirc the dolphin had to basically swim fast and jump into the air to help to force it open. The dolphin wasn’t expected to live long.