As the title indicates, this new short film focuses on the adorably insecure dinosaur toy Rex, an invaluable supporting player across all three films voiced by Wallace Shawn. 

“He’s sick of being the angel of goodness and sensibleness and caution and fear," Shawn told Entertainment Weekly.  “He wants to stand on the side of pleasure and happiness and joy. … I live this drama every day of my life!”

Rex gets his chance to cut loose when Bonnie takes him into the bath, allowing him to essentially throw a party for all the sad baubles who never get to leave the tub.  Mark Walsh, a Pixar animator who has worked onFinding Nemo, The Incredibles, and Ratatouille, explained the idea, saying, “If you’re a bath toy you get really intense playtime. It’s like a party. Then when the water goes down you can’t move. You’re helpless. And that’s pathetic, these guys in bottom of the tub all the time.”

Walsh continued, "What I was going for was, you move to a new town and make new friends, and suddenly you think you have this chance where you can reinvent yourself. I love that Rex, in his sweetness, thinks he can reinvent who he is in the image of a party animal.”

Partysaurus Rex follows the two previous shorts Ken and Barbie's Hawaiian Vacation and Small Fry, which took place in Bonnie's room and a fast food joint, respectively.

Like its predecessors, this Toon will show up before a Disney theatrical release.  In this instance, the short will precede Disney's 3D re-release of Finding Nemo, hitting theaters on September 14th.