How can you look in your own lungs?

I mean, without using an X-Ray. Recently a person was able to do just that, though I expect it wasn’t pleasant. A 36 year old man went into an ICU with acute heart failure. Later that week, he coughed up a blood clot consisting of much of the right bronchial tree. In later examination, doctors saw a small amount of blood in his lung, so this clot was blood that had bled into the bronchial tubes, and clotted there.