Ginormous Growing Shark Grows 6 times its size Animal
Growing animals and other things (brains etc!) that are made to increase in size in water are made up of two polymers. One is poly(vinyl acetate) which keeps the original proportions and shape of the item or creature and the other polymer is polyacrylamide which is the super absorbent polymer. The growing creatures have many teaching applications in science and math, including graphing, drawing conclusions, and measurement using linear, mass and volume. The Growing Creatures Book by Anne Linehan and Betsy Franco details measurement and data collection projects integrating math and science.
Teaching Chemistry with Toys also has science experiments with grow animals.