They could almost be a couple of kids—chasing, tumbling and squealing with apparent glee. Well, almost like kids. For one thing, their squeals would be impossible to hear without the electronic device that lowers the pitch to the range of human perception. For another, black and white lab rats are not what we think of as fun-loving. Yet here they were, chirping up a storm while engaged in a bout of rough-and-tumble play.

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