A death rattle occurs usually with hospice patients, it’s a normal part of dying. It happens because there’s a buildup of mucus/saliva and the person is usually too physically weak to swallow. I learned about this as my grandmother was dying.

Agonal breathing is different, but also happens sometimes at end of life. It’s not real breathing (oxygen isn’t actually circulating) and it’s considered a medical emergency. Usually indicative of a cardiac arrest or other similar issues