There was a graduate researcher at Stanford who was doing a revolutionary, ground-breaking study on the respiration rates of chickens (presumably because they were readily-available at on-campus boutiques).  His goal was to measure the respiration rates of the same chickens under different conditions, such as clucking, picking at worms, attempting like mad to fly over the two-foot fence, what-have-you, and relate it in some obscure way to the way the human body operates.  But he came to somewhat of an impasse regarding how to properly quantify the air intake of said poultry, so he sought assistance from his professor, a fellow biologist.

The biology professor scribbled a few notes on a piece of paper.  "It's relatively simple," he said.  "You need only place the chicken into a chamber filled with a radioactive isotope, then let the chicken breathe in the air for exactly 10 minutes, then cut it open and measure how much of the isotope has been absorbed into its tissues."

"But I can't kill the chicken," the student retorted.

He went to the next door down, which happened to belong to his Physics professor.  Once again the student pleaded his case.

"Ah."  The professor drew a diagram and a graph on the overhead projector.  "You need only place the chicken in an air-tight box with a known volume of oxygen, then time how long it takes it to die."

"But you don't understand!  I can't kill the chicken!"

Being somewhat desperate at this point, the student walked across to the next building, which just happened to be the engineering building.  He found a Mechanical Engineering professor milling about after class.

"Sir, I was wondering if you could help me with a slight problem.  I'm from the Biology department, and I'm trying to figure out how to measure the respiration rate of a chicken WITHOUT KILLING IT."

"No problem," said the prof.  He turned and began scribbling equations onto the front board like a madman.  After fifteen minutes, he was still deriving formulas.  Finally, after all of the chalkboards had been filled, he turned to the student:

"Okay.  Now let's assume we're dealing with a roughly spherical chicken...."