Paper used in this video: 8.5in by 11in sheet of printer paper (approx. like A4 paper - 21cm y 29.7cm)
Finished model: wingspan of 9in (from A4: 25cm)
This video describes how to fold a fantastic action origami model designed by Talo Kawasaki. It's a bat that can flap its wings while at the same time producing some nice noise. You can fold it from printer paper, such as letter (8.5in by 11in) or A4 (21cm by 29.7cm), or rectangles with a similar ratio.
It's the perfect fold for Halloween, and especially fun if a whole group folds it and then everyone flaps it simultaneously. You'll be surprised by how noisy it'll be, just like in a cave when tons of bats fly by!