Reflex bags, also called cobra bags, are used much in the same way double end bags are. They are usually leather bags with an inflatable air sac attached to a weighted floor mount via a spring or other bendable rod. Cobra bags are great for accuracy and timing training, but they also have a steep learning curve. New users to the cobra bag often have difficulty finding combination rhythms and refining the accuracy of their punch. Accuracy, in particular, is important for a boxer to be able to predict the "rebound" of the bag so that they can plan their next punch. This also mimics how a fighter must be thinking punches ahead in a fight. One huge advantage the cobra bag offers is the ability to be moved, unlike traditional double end bags do not.