When your class is cutting up strips of paper to make Christmas ornaments, it’s a perfect time to introduce them to the Mobius strip.
Take a strip of paper about 5 cm wide and 1 meter long, give one end a 180 degree twist, then tape or glue the two ends together. Use scissors to cut down the middle lengthwise of the paper and see what you get, then cut lengthwise AGAIN. Try it again with a complete 360 degree twist on a new piece of paper. Then when you’re done, use the paper for Christmas decorations.