I went to a local craft store and bought a large bag of what looked like brightly-colored styrofoam peanuts. They are supposed to be for children because when you get them a little damp, they stick together and can be used like building blocks. They are made completely from corn starch and are non-toxic and biodegradable. And, even better, they were really cheap!! I got a large bag of them for about four bucks. My U2, Gizmo, loves them and so does my father's CAG and Quaker!