This is the popular Bird/Cage Optical Illusion, featured in Tim Burtons movie "Sleepy Hollow". Johnny Depp would twirl it constantly to concentrate and amuse others. I always loved it (especially the cardinal), so i decided to make one just like it. Its actually not very hard, if its done right.
All you need is thick white paper, and some string. I used off-white heavy cardstock paper and brown yarn to give mine an aged look (like the movie). And i also drew on my pictures to look more authentic, but you dont have to.
DRAWING THE BIRD:
Next find a light source to see through your paper (like a lightbox/sunny window/computer screen). You should see your upside down cage through it.
Now you need to draw/trace your bird on, so it fits ONLY inside the cage. Again trace it in pencil, then again with pens and colored pencils.
(Once your done drawing, your pictures should look upright on both sides when you flip it over vertically. Yay! Hard part over.)