There is a very popular trick of sticking pencils though a plastic bag filled with water. The bags are made of plastic known as a polymer or very long chains of molecules the can be stretched around the pencil to form a tight seal. Paper is also a polymer, it is made of long strands of cellulose. So, will this work with a paper bag? How about though a cardboard cereal box? It works on the first day of April (otherwise known as April fools day). Do you know the secret, if so, you can try it out on your friends.
Here's a another video that might help explain how it was done.
The answer to how it is done.... scroll down
There is a plastic bag inside the paper bag, same with the cardboard box, the bags are slightly larger than the bag and the box and fill in to the shape of the paper bag and box when the water is added.
The plastic bags are made of polymers that form a tight seal around the wooden dowel as it is stuck through it. Sticking pencils though a plastic bag is a fairly common demonstration, the bag and the box just hid what is going on inside.