If you don't love Pixar then it's likely you're already beyond hope. For the past twenty years (yes, Toy Story really is that old), the studio's been producing some of the best films that cinema has to offer, animated or otherwise, expertly blending wryly observed humour with incredibly potent emotional beats. Heck, their output has been so consistent that the Academy even created an Oscar category pretty much in their honour. But, on top of all that, they also pack each film with a Pizza Planet truckload of Easter eggs, in-jokes and references for eagle-eyed fans to discover, to the point where they make Marvel's constant foreshadowing look lazy. Long-running recurring jokes, throwbacks to their classic shorts and teases for upcoming films; there's enough hidden in their movies to warrant countless rewatches. Their latest, the sublime Inside Out, is no exception. It's full to the brim with throwbacks to previous films, some of them obvious, some of them so hidden in the background and deeply involved that even going through the film frame-by-frame makes them hard to uncover. Here are twenty brilliant in-jokes and references you simply need to see, including some ridiculously subtle foreshadowing and all the building blocks of a major theory linking the film to the Toy Story Trilogy.