Rats love to chew up newspaper, carboard, and even blocks of wood.
Here is a list of homeade chew toys you can give to your rats.
1. Macadamia nuts in their shell. Or any other hard shelled nut for that matter (try pecans, walnuts, hazelnuts, etc).
2. Cooked chicken or beef bones (that's Statty gnawing one in the photo)
3. Wood chews (preferably non-pine). You can buy flavoured wood blocks from pet stores, or soak some clean wood blocks in juice for flavour. Your rats may also enjoy paddle pop sticks (leave some icecream on it for them!) or disposable wooden chop sticks, and will probably chew on any wooden toys in their cage.
4. Nylabone edibles
5. Hard, low protein, low fat dog biscuits (e.g. Eukanuba Restricted Calorie Rewards)
6. Baby teething rusks
7. Wine corks -
8. Cardboard boxes - these make a handy nest box and chew toy in one.