Expect your kids to carry around this amazing toy for days, showing friends how they can make their trained "octopus" rise or fall at their command. You'll need a piece of colored cellophane, an eye dropper and a clear, squeezable plastic bottle with a screw-on cap (like the kind soda or fancy bottled water comes in).
DIRECTIONS: Cut a skirt of tentacles from the cellophane and insert the dropper through the center hole. Fill the eyedropper with water until it just barely floats upright in a glass of water. Now fill the bottle to the very top with water and place the dropper octopus inside, tightly screwing on the top. When you squeeze the bottle, the octopus starts to descend; when you relax your grip, it rises again.
WHY IT WORKS: Squeezing raises the water pressure inside the bottle, which in turn compresses the small bit of air inside the dropper's rubber bulb. The compressed air is more dense, and the dropper starts to sink. When the bottle is released, the air bubble expands and the dropper floats back up.