When Ann and Mark are talking about Ann's close relationship to Justin, played by Justin Theroux, they are watching Marley & Me (2008) starring Jennifer Aniston. Jennifer Aniston is married to Justin Theroux in real life; however, they didn't start dating until over a year after this episode aired.
The trivia item below may give away important plot points.
While Leslie is on her date with Chris, he compliments her "oven", remarking that she's got ample room in her uterus and "could [have] triplets right off the bat". In Parks and Recreation: Flu Season 2 (2014) it is revealed that Leslie is pregnant, and that She and Ben are, in fact, having triplets.