Pixar has made plenty of beloved movies at this point (20, as of 2018), and they continue to create more. One of the most highly anticipated is Toy Story 4, and in the recently released trailer, Pixar made a reference to one of their earliest films.
Monsters, Inc. was another of Pixar's great successes; the interesting premise and lovable characters combined to create a film that many still enjoy today.
Boo is one of those lovable characters. A human girl that Sully was supposed to scare. She ends up following him back to Monsters Incorporated, and adorable hilarity ensues.
In the new trailer for Toy Story 4, a girl who looks remarkably like Boo (complete with signature pigtails) can be seen at a table behind Bonnie at school. Bonnie is the human girl who now owns the titular toys.
You can view the trailer below:
Toy Story 4 | Official Traileryoutu.be
Fans were shocked at seeing Boo in the trailer.
A second "reaction" promo with Ducky and Bunny, new characters voiced by Kegan-Michael Key and Jordan Peele, was released as well. In it, Ducky and Bunny comment on the fact that there will be a new Toy Story movie, and their love of the series.
Buzz also makes an appearance as the two attempt to mimic Buzz's famous line "To infinity and beyond!" They both get the line hilariously wrong, and eventually Woody and Buzz show up and correct them; the whole trailer is delightfully strange and totally meta.
You can watch that here:
Toy Story 4 | Teaser Trailer Reactionyoutu.be
Toy Story was Pixars's first movie, and a resounding success. As such, they've put a lot of work, and a lot of love, into the sequels. It is exciting to think about what they will do next, and there are many people eagerly awaiting the release of Toy Story 4 on June 21st.
Good Bye GIF 
Make It Rain Money GIF 
Look Whos Talking Now Omg GIF 
Save Schitts Creek GIF by CBC