Cumulative Record. Chapter 10: The Experimental Analysis of Behavior. Quote 3

In studying such [operant] behavior we must make certain preliminary decisions. We begin by choosing an organism—one which we hope will be representative but which is first merely convenient. We must also choose a bit of behavior—not for any intrinsic or dramatic interest it may have, but because it is easily observed, affects the environment in such a way that it can be easily recorded, and for reasons to be noted subsequently may be repeated many times without fatigue. Thirdly, we must select or construct an experimental space which can be well controlled. (p. 133)