Demonstrate how easy it is to squeeze out the contents from the can, then pick a volunteer and ask them to try to put the cheese back into the can. Of course it is impossible. Angry, sarcastic words, derogatory names, or mean comments are very easy to say. But it is difficult and maybe impossible to fix the damage done by idle or angry words. You could use any other object that squeezes out of the top like toothpaste or whipped cream or something like that. The author chose the cheese because you can spread it on crackers at the end of the lesson. Source: http://www.geocities.com/Heartland/Flats/4746/lessons.html