Let’s see.... as I recall from my junior high days, a little potassium iodide, a little ammonia. Filter the precipitate and let it dry. Take crystals and put them where your sister is bound to step.
Sister crying, getting whomped on by Dad.
Yes, I remember it well. Crystals drying on the picnic table in the screened in porch in the back of the house. Went out front and, when I came in through the front door, I accidentally let it slam. You can imagine what happened next.
Years ago, you could actually walk into a pharmacy and buy iodine crystals themselves.
Them, plus the ammonia, make a heck of a BANG!!!