Processes of diffusion of oxygen can be described in a formalized and simplified manner in formulas such as Fick's laws of diffusion. For a sound understanding of the interconnections of anatomical structure, biological function, and environmental factors in a living system, however, real-life case studies need to be employed to explore what is captured in the equation and what is not, and which other structures and behaviors may play a role in respiratory physiology. I use four anuran examples to illustrate, starting with Fick's first law, respiratory processes as influenced by surface-area-to-volume ratio and turbulence in the surrounding medium.