There is a pause in the print. During that pause you can fill the cavity of this print with fine glitter. Once you resume it will seal it closed. Give it to someone and tell them to snap it in half to open it. Glitter will get everywhere.

would work well if you put good stuff like rolled up money in a few and just have one secret one with glitter.

If you do this to someone make sure it's someone you are okay with not talking to for a while. Glitter is evil and they will hate you