This supplemental lesson on the Columbian Exchange has shocked my students for four years into remembering the Columbian Exchange, especially the effects of Smallpox on the Native Americans. The teacher slyly infects students with "Smallpox" at the beginning of the lesson, and a blacklight will reveal at the end who was "infected". This is the lesson that my former students from years back see me and ask, "Hey Mrs. Andersen, are you still infecting students with Smallpox?" I always look forward to teaching this lesson year after year!
If teaching the Columbian Exchange is not part of your objectives, this lesson can be modified to teach about the healthy habit of washing hands! (You never know what's lurking around on them!)