A conversion I had during residency:
Resident: "Do you notice anything wrong with this chest film?"
Me: "Um, there's a GIGANTIC effusion on the left side?"
Resident: "Yeah, obviously. But what else?"
Me: "I'm assuming it's what that arrow on the right is pointing to."
Me: (squinting) "Oh, it's a pneumothorax, right?"
Resident: "Yeah, I mean... would you have seen that? It's practically invisible. That's why I could never be a radiologist."
Me: "Well, you might notice it if you were looking for it. What was the film done to look for?"
Me: "See, there you go."
Resident: "Do you want to hear a terrible story? The team tapped this patient's lungs to try to get at that effusion. But they tapped the wrong side. So not only is there still a huge effusion, but now the patient has a pneumo on the other side."
Me: "Haha... that's funny. Well no, it's not really funny. But it's... well, it's ironic."