The passage Chris reads at the end of the episode is from "Swann's Way", Volume One of "In Search of Lost Time" (originally translated as "Remembrance of Things Past") by Marcel Proust.
Ed's movie reference: Alice Doesn't Live Here Anymore (1974).
Joel calls it 'natural immunity' when someone does not react to poison ivy. This is one of those cases where the English language doesn't work well. Poison ivy itself does not cause the itching and rashes and blisters. Our immune system overreacting causes these symptoms. Those who do not have an immune response do not get itchy blisters. Those who have a hyperimmune response suffer.
The opera aria playing as the episode opens is, "La donna e mobile," from Giuseppe Verdi's "Rigoletto."