 Heschel insists that ultimate meaning can be sensed beyond a naturalistic understanding of natural phenomena, and that such meaning is mysterious and awe-inspiring.In "The Tangled Wing", Melvin Konner reviews the biologist's view of this pain and pleasure of learning.He notes that "If the problem is too unfamiliar, it will evoke attention; if it is difficult but doable, it will evoke interest, attention, and arousal and, when solved, it will evoke pleasure, often signalled by a smile" (p. 242).