This is a very simple illusion to make but is still surprisingly difficult for your mind to get around. If you hold this card by opposite corners in one hand and spin it, the arrows drawn on card all point up. If you hold it with the other hand, the arrows alternate between pointing up and pointing down.
Pencil, pen, or Post-it® note
Cut out a small square from card stock.
Cut two small arrows out of the sticky part of the Post-it note.
Place the first arrow on the card so the arrow is parallel to the sides and points up (away from you, depending how you look at it).
Hold the square with your thumb and your forefinger on diagonally opposite corners so the card can spin around. Spin the card and place the second arrow on the back side of the card facing up.
Transfer the card to your other hand and hold it between your thumb and forefinger (but this time on the other two corners) and spin the card. This time the arrows alternately point in opposite directions as you spin it.