Cascabel are much milder than chili de arbol. More of a earthy, woody flavor. Used more for flavor than heat.Here is a cut and paste:
Species Name: Capsicum annuum.
Color: Green maturing to red, dries deep reddish brown.
Shape: Bell-shaped rounded pods.
Description: Smoky, woodsy, slightly bitter tannic flavor.
Scoville Heat Units: 1,250-2,500
Other Names: Chile Bola, Rattle chile.
Related Cultivars: Mirasol.
Most Commonly Grown In: Mexico
"Cascabel" in Spanish means "jingle bells", and the chili pepper gets its name from the fact that when dried, shaking the pepper makes the seeds inside the pod to rattle.