Chekhov's Gun: To compensate for the inability to get a security diary for her, Bart gets Lisa a laser pointer for her birthday. At the climax of the episode, Lisa uses it indirectly against Dexter Colt.
Clear My Name: Homer and Lisa have to clear their names when a detective steals animals from a lab and frames them.
Credits Gag: Bart steals Lisa's new diary, which shocks unauthorized users who try to open it, and tricks Homer into an attempt to read it as a bedtime story.
Mega Meal Challenge: The P.I.'s bill includes 40 dollars for a steak. The detective explains that it'd be free if he managed to eat it all.
Nobody's That Dumb: When Lisa is framed for a crime she didn't commit and the cops sees her and Homer flees when they arrive to arrest her, Chief Wiggum said something that even his own son, Ralph, knew the answer to:
Chief Wiggum: (to Marge) Would an innocent person flee? (beat) Chief Wiggum: No, really. Tell me. I honestly don't know. Lou: Chief, no. Ralph: Even I knew that. Chief Wiggum: Yeah, yeah, I'm not... I'm not good.
Noodle Incident: Homer chopping up Bart's skateboard with an axe for the insurance money.