1. Start with a square. Fold side to opposite side. (The origami term for this is a book fold. Any fold produces what is called a valley fold on one side and a mountain fold on the other. After doing some origami, the students will probably develop their own jargon to satisfy the obvious need.) Unfold. Repeat this with the other two sides, making a cross. Turn the paper over and now make two diagonal folds. (The origami jargon for this is a diaper fold. This could be told to the students for its historical significance.)
Water bomb base: collapsing of initial
valley and mountain folds
2. Place the paper on a surface so that the diagonal folds are mountain folds. The paper assumes the shape of a tent. (This is the same as the top part of the business card frog, so you can ask students if they have seen anything like this before.) Looking at the paper from above, you can form it into a 4-pointed, star like figure. What can you say about the symmetry? Push the sides in more and let the paper collapse into a flat triangle. It is now bilaterally symmetric with two flaps on each side.
The base is used to make the Water Bomb and the Water Bomb Modular.