It's not Friday yet, so ITIAYAQD!

[cyrano]

So does anybody remember, back in school, the kids would fold up a piece of paper in a certain way and then open and close it, open and close it, until finally they'd abruptly decide to stop, and then you'd discover what your favorite color was or how many kids you were going to have when you got married or the name of the therapist you'd spend years describing your childhood and family to?

What are those called, and how do they work?