Open 123D Design at http://apps.123dapp.com/design/ and build your design. I only used two primitive shapes for this one: 8 spheres, and 2 domes. Save your model. Close 123 design.
Step 2: Optimize it for cardboard
Open 123d Make at http://apps.123dapp.com/make/ and load your previous project. Then download sheets.
Step 3: Fabricate
print your sheets, draw the outline on cardboard, and glue the pieces together! or if you are laze like me and have access to a 3D printer, 3D print your bunny. You can find my design here: http://www.123dapp.com/smb-123D_Design/Bunny/1251480.