*Masking tape or duct tape. Duct tape is better to keep light out from cracks. Otherwise,use a black felt marker on tape to keep all stray light out of box.
*Single edge rasors or a breakable thin rasor blade work well. For a children's safety version, use the opposite edges of a credit card cut in half. It will save you a lot of money!
*The LED's are fun to observe as is a compact flourescent light. The laser pointer is dangerous and should be used with care and only to illuminate a translucent plastic bag covering the slit.
- Any CD that you don't mind damaging