Alright. Here's a fun one to do with a cup from the water cooler. All you tell them is they need to take a cup. You should use an empty cup for this. Take a bill, a dollar bill works better. You can use an index card, but a dollar bill is still better. You tell them they have to balance the cup on the bill. If you showed them the coin thing they're probably going to try and do it like that, but the best way to do is you take the bill and you give it a bunch accordion folds like this so it is just like that. Then you can put the cup right on top of it. If your folds are even it'll stand right up. That's how you balance the glass right on the bill.
