"Or," von Hacklheber says, "suppose she looks at the cage, and sees how the balls are distributed inside of it, and then closes her eyes. She will subconsciously reach toward the E and avoid the Z. Or, if a certain letter has just come up recently, she will try to avoid choosing it again. Even if she cannot see the inside of the cage, she will learn to distinguish among the different balls by their feel—being made of wood, each ball will have a different weight, a different pattern in the grain."