<human>:  What is the difference between a grass-mattress and a spring-mattress?
<bot>: The main difference between a grass-mattress and a spring-mattress is the type of material used in their support system. A grass-mattress typically uses natural grass such as wheat straw or horsehair for support, while a spring-mattress uses metal coils or springs. Grass-mattresses are often more breathable and provide more support, while spring-mattresses can provide more cushioning. Additionally, grass-mattresses generally last longer than spring-mattresses.