Creating a "rubber" egg is a great science experiment that requires very few materials and very little cleanup. This experiment demonstrates the chemical reaction occurring between the calcium carbonate in the eggshell and the vinegar (an acid). It is a lot of fun for children and it gets them motivated and interested in science.
Hard-boil an egg and place it in a jar.
Pour vinegar over the egg and fill up the jar. Place the lid on the jar and allow the jar to sit for three days.
Remove the egg from the vinegar. The eggshell will be gone, leaving a thin membrane around the egg. The egg will feel very rubbery.
Try bouncing the egg on a table. This won't work if you throw the egg too forcefully or drop it from too great a height, but it will make small bounces.