I like having them write down things that they wouldn't have really thought about until that moment.
Here's an example from The Jerx. This is an application for a NW but you could easily apply it to a billet peek. You ask them "If you could safely eat some item in the world
that isn’t edible, what would you eat?". Have them write it down and then peek it. Have them open their mouth and pretend to chew or something and then divine what their answer is.
He calls this
"The Unknown Personal" and it's really fun to play with.