All you need is:
-a raw egg
Carefully place the raw egg in the glass, then pour vinegar into glass to cover egg. Let egg sit for a day or two until egg shell is dissolved, leaving the membrane. Remove egg from vinegar and clean. The egg will feel rubbery (like a bouncy ball).
Lift the egg 1-2 inches in the air, let go and watch it bounce. The egg will also be much bigger than a normal raw egg due to osmosis of vinegar moving through the membrane into the egg. When you are ready for some messy fun, lift the egg a little higher in the air and let it go….SPLAT!