Consider the normal use of running for an animal: running for prey, running to not be prey... Yet, we know as humans that running can be enjoyable. For an animal, running is more often associated with hunger and fear of being eaten. I propose the running wheel presents to the animals a rare "place to run safely". Normally, running transports an animal into new, potentially unsafe locations. This running wheel was both in an enclosure, and the wheel itself offers protection from attack. I wager that 18 minute run was a mouse experiencing the joy of running without fear for the first time, and was exhilarated.