This willow ball is great for cats as well as rabbits. The willow is tightly woven, ensuring that this ball will last a long time. The natural willow has not been peeled, so bunnies who like to nibble the bark will have just as much fun as those who like to roll and/or toss their toys in the air. The balls range from 3.25 to 3.5 inches (8.3 to 8.9 cm) in diameter and are hollow inside.