Place two hula hoops on either the floor or chalkboard, making sure they overlap forming a center section.  Label each section of the diagram to show what is being compared.   Have students write two facts learned about the Effigy Mounds, its past inhabitants, plants or trees, etc. on index cards.  Place the cards in a pile.   Then have students take turns picking a card and deciding which part of the Venn diagram it belongs in.  Using the completed diagram to compare and contrast the items labeled.

After completing the hula hoop activity, follow up with a writing assignment on the topic.  Ask students how they would organize their essays.  Help them see that in completing the Venn diagram, they have actually placed related ideas into groups and established an organization which can be translated into a "compare and contrast" essay.