- a pencil
Hand someone in the class a pencil, and ask them to "try to drop it" once the person drops the pencil, pick it up and say, "No, maybe my instructions weren't clear, I said TRY to drop the pencil". They might act confused, and maybe drop it again if so just repeat the process, but if they hold onto it and do not drop it, then say, "No what I wanted you to do was to TRY and drop it!"
Once the person gets confused or irritated with you, say thank you, and retrieve the pencil, you can ask another to try the same thing and see if anyone does it any different. When everyone keeps dropping it or holding onto it, tell the the punch line...
"There is no such thing as 'Try' you either do or you don't. So let's DO what we are asked to do and not give the excuse that 'We tried'."
(Jenny - This is great for challenging a class to apply the messages you have taught during class.)