There was so much swelling, and no veins were available, so the docs had to do a central line. April tells the panel hopelessly that everything was failing at the same time. Cristina arrives as Cathy starts to code, and they try to shock her to get a heartbeat back. Things only go from horrifically bad to unimaginably worse when Reed notices that she's bleeding into the tube coming from her throat -- she's bleeding out on top of everything else. As Reed sits facing the Big Three, something clicks in her mind and she tells them, horrified, "I know what happened. I know why she died."
Back in the ER, blood is streaming from Cathy's nose and is pooling everywhere. The doctors are all yelling and trying to help, but the yelling is intermingled with the steady alarm of her heart not beating. Derek wades into the chaos and after doing some yelling himself finally manages to quiet everyone, telling them that it's over. He then tells someone to call it, but no one pipes up, even when he asks whose patient it is.
Back in the present, Reed comes out of the panel room and tries to walk away through the others but April grabs her arm. With tears in her eyes, Reed says that she's so sorry just as Richard comes and calls April inside. April goes from confused to scared in the blink of an eye and asks what Reed said, but Reed just shakes her head and runs off, so April turns and goes inside.
Once inside, she looks like she's about to hurl while Richard says that he doesn't know her, but that Reed just spent 20 minutes telling them what a good doctor she is, which is also what all of her school records and recommendations show. He tells her that he believes she's good, but when she starts to speak he cuts her off and says that therefore, she should be able to tell him what caused Cathy to die from multi-system organ failure. April goes through everything, with an accompanying flashback for each -- she cites Cathy's burns and collapsed lung (accompanied by a totally gratuitous shot again of Lexie about to insert the chest tube -- thanks, Show!) but Richard just asks her why Cathy's lungs would have failed. Hannah gets flustered and Richard keeps up the rapid-fire questioning, finally asking what might have caused her restricted airway. April tells him that soot or smoke inhalation would do it, and when Richard asks how her throat looked, April catches herself and everything seems to click into place. She tries to defend that Cathy wasn't hoarse or coughing but Richard asks again what it looked like, and when April finally crumbles we flash back to her examining Cathy. She's about to look in her throat when they are distracted by Mr. Axe Chest. It was a pretty obvious moment earlier in the episode -- even though I didn't know the medical reason for why that led to everything going wrong, it was telegraphed that it was where everything started. That said, it didn't take away from this being a really good, well-done episode.