Bird-call Window provide the collaborative puzzle play as the poetic expression. By imitating a bird call, the viewers can summon geometric shapes to play silhouette puzzles onto a curtain . When a puzzle is solved, the silhouette turns to a bird. It flies into the virtual world and then it may sing, preen on the trees, or fly around but they eventually fly away and disappear. Therefore many puzzles are solved in a short time, the various colorful birds might enliven the scenery beyond the window.