You will need:
A Kinder Egg
Some string (optional)
Dremel multi tool
Hot glue glue (optional)
And most important, KITTY TREATS!
Step 1: 1st, Eat the Chocolate and Assemble the Toy.
You'll be left with a yellow plastic egg, draw an outline of the size hole you want. Make it just a bit bigger than the kitty treats you want to use.