I had not seen this before, but it makes a great measuring and comparison lesson. Go to How to Pass Your Body Through a Sheet of Paper for step by step instructions on how to cut the piece of paper.
Ask students if it is possible to walk through a sheet of paper. Of course they will tell you "no." Follow the instructions and cut a regular sheet of copy paper so that you can pass through it. Have students talk about what they noticed and why they think the way they do. Ask them what will happen if you cut a larger sheet of paper. Have them make predictions and discuss why. Cut a large sheet of chart paper so that you can walk through it. How did it change from the small sheet? Why? Ask kids these questions. Have them make predictions about how many classmates will fit through it. Check your answer.
You can find printable instructions from Family Fun.