...from a certain popular Disney/Pixar movie.
Which of course you can write about if you would like to.
Funnily enough, though, I didn't have an instinctive response to this prompt. Nothing that immediately came to mind. So I had to think. And here is my question to help you:
What is inside you (thoughts, feelings etc) that should be out to the world, but aren't? Do you have anything inside you that is out, but that you didn't want to be? Or maybe you are relieved that these 'inside' feelings are finally 'out'?
A sonnet comes to mind, thanks to the volta (or 'turn') at line 8, which marks the turning point between one set of ideas and another.
For an alternative take on 'inside out', here's Groucho Marx:
In the meantime, read other participants' poems, share the #octpowrimo hashtag on social media, and add your link to your own poem in the comments below.