Have a 'volunteer' student sit on the floor with a baking pan in front of them. You tell them

that they are to grab as many candies as they can in 1 min. but they have to keep their eyes on the pan; no looking around. Have another student time.  Stand beside the student and start dropping various sizes and colors of candy from a bowl one at a time into the pan. The student will become very focused on the pan and grab the candy as fast as they can. Only drop one candy at a time, student grabs it, you drop another. After about 7 or 8 candies have been snagged drop a raw egg onto the pan. The student will grab the broken egg. To make this work you have to have a container for the candy and egg that the students can't see into and you have to keep the volunteer busy grabbing candy - no long pauses between candy. (the timer is really just to convince the kids that you really are playing a get the candy game).  After the class noise died down, we talked about: how the candy wasn't really good for you but not really bad either and how those kinds of things can become such a habit that you don't even notice when they turn bad; how the student thought she could trust me so she didn't pay much attention to what I was giving her instead of checking for herself; I'm sure you could think of applications that would be appropriate for your class. I was just amazed at how well it worked.