In the movie world they're known as Easter Eggs - when the film's creators hide something in the movie that's an intentional inside joke.
Disney's Easter Eggs usually consist of characters from different Pixar movies appearing in other Pixar flicks.
And now, just in time to rescue us from a serious dose of the January blues, Disney have released an amazing compilation video revealing a boat-load of new Easter Eggs in movies like Inside Out and Finding Dory.
Whoever spotted these had a very quick eye!
