The Cross Slider is Kyjen's most innovative, and challenging, puzzle toy yet! Simply drop the Hide-A-Treat ball into the top hole of the slider base then encourage your dog to retrieve it. By sliding the base across the floor, dogs are able to move the ball around inside. The goal is to free the ball through one of the tunnels. Once free, the ball dispenses treats naturally throughout play. Refill and re-insert the ball to repeat the fun! Initially, all four doors can be left off the base, allowing four tunnels through which the ball can exit. For increased difficulty, up to three doors (included) can be added, leaving only one tunnel open to free the ball. The Cross Slider works great with tennis balls too!