A metre long piece of 30cm wide single sided corrugated cardboard rolled up to prevent unwanted creases. It is made of natural recycled brown kraft paper and thereby really useful to have on hand when making DIY pet toys as it is an environmentally friendly, textured, thick paper that is safe for them to shred.
 

One of our bunnies goes crazy for it. As though he has been put on Earth to do one thing, tear corrugated cardboard apart. However, the other one isn't phased by it. Different strokes. How does your bunny roll? Corrugated Cardboard roll?