To share with the class:

• several copies of the 31-page picture book, Zoom, by Istvan Banyai, one per group; the number of available books determines the number of teams; take each book apart for the activity; keep one intact book as an answer key; paperback for $8 at Amazon; 
• (optional) access to a laminator machine and laminating sheets, to laminate the Zoom book pages so as to better withstand handling by students
• Duck/Rabbit Visual Aid, one printout to show the class; same as Figure 1; also available at https://commons.wikimedia.org/wiki/File:Duck-Rabbit_illusion.jpg
• small blank paper booklets, one per student; each made by the teacher in advance from one to three 4 x 4-inch (~10 x 10-cm) squares of paper folded and stapled in the fold (see Figure 2); provide more pages for higher grades; see instructions in the Procedure section
• pencils, colored pencils or crayons
• measuring tools, such as unifix cubes for younger students and rulers for older students