Here is what happened to the egg, the vinegar breaks down the egg shell because the egg shell is made of calcium carbonate and the is vinegar is an acid!!! The experiment took longer than it said it would, instead of 2 days it took 5 days.
Air coming out of the egg. The egg is porous, so lets the vinegar inside. The egg was like a balloon , it felt like one and when we put a knife in it, it popped.
Thanks to Blue Yonder - Book of days January Issue for this experiment