Two cans are shown to demonstrate how they can be used to boil water. The first can has a hole cut out of the bottom and one for the top. The second can is cut at the top like a cup and the bottom left whole. Its placed on top of the first can. Cotton balls and petroleum jelly are inside of the bottom can, then lit with a match. Several sticks are used as kindling to keep the fire going. After about five minutes the heat of the flame on the bottom of the top cup causes the water up top to boil.