"It's a pit where we throw stuff that isn't worth the space it takes up other places anymore- obscure knowledge, unimportant memories, imaginary stuff that isn't being used anymore, and so on. Stuff left there mostly eventually vanishes, some things quicker than others."

"Space is limited?"

"Yes. Around nine square miles."

"By... what?"

"Riley's mind is round- go far enough and you come back to where you started."

"So it's not enclosed, it's space-warped?"

"Yes."

"Huh. Has it always been that size?"

"No, it gets bigger over time. But only slowly."

"Huh. What does an imaginary person who doesn't fall down and doesn't get imagined any more do?"

"Bing-Bong traveled around Riley's mind and collected old memories after Riley stopped imagining him, but I don't know if that's normal."

"Don't explore much?"

"I don't. It always seemed like too much effort. And too much of an imposition on everyone. And recently I've been busy."

"- are you yourself generally sad?"

"Yes."

"Is... that... okay with you?"

"I wish I had less to be sad about, but I don't think I could not be mostly sad and still be who I am."

"I guess that makes sense. Are the other four the same way?"

"Yes- Joy is happy most of the time, Fear is scared most of the time, and so on."

"Sounds rough to be Fear."

"Yeah."

"How much of the other stuff you've mentioned was there when Riley was born and when'd the rest of it grow in?"

"The Dump was there from the beginning. So was Long-Term Memory but it used to be a lot less well-organized. The Dream Studio was there from the beginning but used to be a lot smaller and less well-supplied. Somewhere that would become Imaginationland existed by the time we were one, but it was also pretty small and simple to start with. Abstract Thought's newer, it was only built about two years ago."

"How did stuff get more organized and built up, did people do it or is that just one of the things that happened? And what happens in Abstract Thought and who built it?"

"Mind workers organize and improve stuff, and build Abstract Thought. Abstract thought-"

she winces.

"Basically it takes concrete concepts like, say "these apples" or "these trophies" or "mom and dad" or "Cathy's mom and dad" apart into more abstract ones like "groups of objects" or "parenthood" and uses the more abstract concepts to figure stuff out, sometimes stuff that will apply across lots of different sorts of situations."