“They approached the bar, pressed it with a forefoot, quickly swung around, sometimes looking up at the experimenter, and waited motionless a second or two” (p. 254). Again, this is what Guthrie might have predicted, but that the behavior was conditioned by contiguity and protected by removal from the chamber is impossible to prove, because there is always the possibility that reinforcement of some kind was present (for example, in the procedure of handling the animals, which so frequently in their lives has been paired with feeding).