You’re tellin’ other things, but your girlfriend lied
You can’t catch me ’cause the rabbit done died.

 The lyrics above (from Aerosmith’s 1975 single “Sweet Emotion”) may seem pretty obscure to modern audiences, but they actually refer to the Aschheim-Zondek Rabbit Test, one of the earliest accurate tests for human pregnancy. The test, developed in the 1930s at the University of Pennsylvania, involved injecting a laboratory rabbit with a woman’s urine. The presence of human chorionic gonadotropin (hCG) caused the rabbits ovaries to change, which could be observed (after surgically extracting the organs).

Because the procedure to examine the organs involved killing the rabbit, a widespread misunderstanding of the procedure led to the phrase “the rabbit died” as a euphemism for being pregnant. In truth, the rabbit died either way, and while it was possible to complete the procedure without killing the rabbit, that made the process much more expensive and difficult, and consequently, a lot of rabbits died.

Later, scientists found a way to test for pregnancy without the need to dissect a rabbit: injecting female African clawed frogs (Xenopus laevis) with pregnant women’s urine stimulated the frogs to produce eggs, an obvious process that didn’t involve killing the frogs.

The advent of modern immunoassay methods now allow doctors to measure hCG directly from the blood or urine of a woman, eliminating the need for either a dead rabbit intermediary or an ovulating frog.

While no one (except perhaps Aerosmith fans) think much about the Rabbit test anymore, Xenopus frogs like African clawed frogs now rank among the most-studied model organisms in science, and even to this day, human growth hormones are used to stimulate the frog to reproduce easily in captivity.

So a test for human pregnancy that resulted in the deaths of countless rabbits is now used to help frogs reproduce more easily. How’s that for recycling?