Meanwhile, Howie explains sadly to Carter that a bunch of jockstraps convinced him to change the chemicals. "It was only supposed to be a small exothermic reaction," he mutters, but Mr. Sutherland changed the experiment, and Howie "didn't have a chance to warn him" about the switch. "This wasn't supposed to happen," he protests miserably, "it was just a joke!" At that moment, Mr. Perez materializes in the doorway of Howie's room and greets him with, "You little son-of-a-bitch." Carter tries to warn him off, but Mr. Perez snarls that his son "is blind because of you." Howie argues that it wasn't his idea, "Nathan and his friends told me to do it," and Carter gets up to remove Mr. Perez from the room, but Mr. Perez doesn't like that idea and he throws Carter into a window to illustrate his point. Every single week, glass gets broken in the ER -- shoot-outs, fistfights, med students kicking their advisers into walls while practicing Tae Bo, vengeful relatives of patients slamming doctors into mirrors -- and yet we never see either a glazier or an empty mirror or window. Did you ever notice that? Well, now you will. Anyhow, Mr. Perez gets Carter down on the floor and starts throttling him, and Mark runs in and tells him to get off, but Mr. Perez pushes Mark away, and Mark morphs into Mean Mark Greene and yanks Mr. Perez away using a choke-hold. Carter leaps to his feet, only to hear Chuny yelling, "Sir? Sir!" at Mr. Perez. Looks like Mark morphed into Justin Volpe instead, because Mr. Perez isn't breathing. They lug Mr. Perez to a nearby bed and prepare to intubate him, and Carter thanks Mark for "pulling him offa me," and Mark says grimly, "Just get the tube in, Carter," as a worried Howie looks on. Carter and Mark try to intubate, but it isn't working and they can't figure out why; long story short, Mark broke his larynx, so Mark does a tracheotomy instead, which works. Carter compliments him, "That a nice save," and Mark makes an "I doubt the legal department will agree with you" face and says, "Yeah."