When Lucy and Gru are reviewing Paradise Mall shop owners (suspects), the owner of Stuff-A-Bear (a satire of Build-A-Bear) overstuffs a bear and it explodes, making an expectant little boy cry. The boy is the same one that Gru made cry with a popping balloon in the beginning of the first Moi, moche et méchant (2010).
When Lucy Wilde gives Gru a phone number to reach her, it is clearly visible as 626-584-5723. Calling that number reaches a recording of Kristen Wiig in character, with her outgoing voicemail message. However, the voicemail box is full, and you cannot hear her recording. This number is no longer in operation.
The actors are filmed the entire time they read their parts. Their facial and hand expressions are used on screen. Steve Carell's wife had fun pointing out the expressions in Gru that reminded her of Steve.
One of the Minions calls the 21 fart gun salute for Dr. Nefario by saying "Pado," which is the Hindi word for fart.
When Silas Ramsbottom shows Gru a video of a rabbit being injected with mutation serum, the name tag of the scientists in the video read "COFFIN" and "RENAUD" - a reference to directors Pierre Coffin and Christopher Renaud.