Nelson and Lisa hold hands, referring to the episode where Lisa dates Nelson. They also discuss the time they were dating.
It is heavily implied in the end that the two still have feelings for each other. This was also seen at the end of "Lisa's Date with Density", where they break up, but on good terms, and even smile at each other.
Lou went undercover in Fat Tony's mob (which Homer will do in another episode this season).
Wiggum accidentally exposes (or almost exposes) Lou as an undercover cop when Lou is at dinner with Fat Tony and the rest of the mob.
This is the third time when Wiggum has outted someone going undercover in Fat Tony's mob. The first time was in a Simpsons clip show where he told Homer they had a guy undercover who he then pointed and waved to that guy what's was standing in front of Fat Tony. The second time was when Bart went undercover to buy fireworks and Wiggum called out Fat Tony's name exposing that Bart was wearing a wire.