What are cool and inexpensive home science experiments I can do to blow my child's mind?

ProjectA Quora user posted the following question: "What are cool and inexpensive home science experiments I can do to blow my son's mind?" He got a bunch of great answers, including this video of a girl explaining how to suck a hard boiled egg into a bottle. She is delighted with the results, and I laughed right along with her. Other ideas include a homopolar motor, collecting micrometeorites from your roof, and making a pickle glow.

What are cool and inexpensive home science experiments I can do to blow my child's mind?