Disney movies are always full of easter eggs. Recent films have been absolutely overflowing with references to previous Disney movies. However, one Big Hero 6 easter egg was only recently uncovered as it actually made reference to a movie that came out later. It was just discovered that Big Hero 6 actually contains a Zootopia easter egg. Of course, nobody noticed until after Zootopia came out. As it turns out, the design for Honey Lemon's cell phone case, a fox wearing a tie, was an intentional reference to Nick Wilde, the fox that wears the same in Zootopia. Big Hero 6 art director Scott Watanabe explains...
Early on, Honey Lemon's phone case was designed to look like a bear, to conjure up a "honey" connection, but we came across a few similar designs in our research. I began to think of other animals and Nick Wilde, the fox from Zootopia (which was in production at the time), came to mind. Thought it might be a fun Easter egg for fans to look out for in the film.
Most people probably didn't give Honey Lemon's phone case a second look while watching Big Hero 6. At that point, nobody was talking about Zootopia. However, since the film was in production at the same time, Disney artists had seen what was being worked on. According to Oh My Disney, the phone case design was based on early concept art of Nick Wilde, which explains why the character and the phone case have a resemblance but are not identical. By the time Zootopia was done, Nick had gone through some design changes. Big Hero 6 never gives you a great look at the image on the phone case but you can see it well enough in the screenshot below.
We do get a decent shot of the phone side at one point, which gives us the fox shape, and shows that the case includes a tail.
Zootopia would pay back the easter eggs when it came out last year. There are at least two references to Big Hero 6 within the film. The Lucky Cat Cafe, which is run by Hiro's aunt in Big Hero 6 is seen in the background of one scene, we assume that one is actually run by cats. There's also an image of the city of San Fransokyo on a calendar in the Zootopia Police Station. Zootopia would also continue this trend of referencing future Disney movies. Among the bootleg DVDs being sold by Duke Weaselton are references to Moana which came out last fall, and Gigantic, set for release in 2018. Moana in turn also had a reference to Wreck-It Ralph, a film with a sequel coming out in about a year. The cycle continues.