House knows Riley has a history of absenteeism and, in a desperate attempt to get out of doing the lecture, accuses him of malingering. Cuddy assures House that Riley has nausea and vomiting, but House asks her if she has actually seen "the spew". She dismisses his concerns and he agrees to do the lecture in exchange for being let off two hours of clinic duty.
During the lecture, House uses Riley's handmade "World's Greatest Dad" mug to get himself some water, and after taking a sip immediately spits it out and stops drinking from the mug. After the lecture, he asks how the "World's Greatest Dad" would allow his children to use lead based paint - Riley has heavy metal poisoning from lead glaze on the mug, which explains both his current symptoms and his ongoing absences.