For those who don't want to ruin a good book for a safe...
2 Tennis balls
1 Box cutter or small swiss army knife
Okay let's get started!
Step 1: First (and Last) Incision
Start by making a 1.5 inch (about 4cm) cut along a green felt side of your choosing. Be very careful not to cut yourself! Set aside.
Step 2: Picking the Fuzz
Next, grab the second ball and start pulling some of the fuzz off with your fingers. Get at least small handful of it. Set aside the second ball.
Step 3: Roll the Fuzz
Place the fuzz between your palms and roll into one big string of fuzz.
Step 4: Insert the Fuzz
Now take the first ball and squeeze the sides to open up the "mouth" of the ball. Close and adjust so that the incision blends in with the rest of the ball.
Step 5: Done!
Now you can insert valuables and have them disguised as a lovely green sphere of felt! (My next Instructable may feature a wall display for these tennis ball safes--a most unlikely hiding place for your treasures!)
If you liked this Instructable, please vote for it in the protected contest!