Close the fold on a prepared surprise, pass it over, and let the next opening release it once.
Choose what pops out, write a line of your own, close the phone and hand it to a friend. It goes off once, the moment they open it. Six effects: confetti, applause, a plain note, a spring snake, balloons and fireworks. Confetti, applause and the note are free; a short video unlocks any of the others for one use. Pick gentle or lively; gentle is the default. Nothing here is built to frighten anyone. You can also take one photo of their reaction. It stays in memory, is shown to the person in it, and is saved only if they choose to keep it. On a phone that does not fold, a tap sets it off instead. The free version shows an ad after the prank has finished. A single purchase removes every ad and unlocks all six effects. You never need to close the phone hard.