Before the 1930s, women who wanted to know if they were pregnant only had one reliable option: the rabbit test. Old-timey doctors had figured out that injecting the human pregnancy hormone into other animals triggered ovulation, so these medicine men started keeping entire farms of rabbits and mice to stick with pee syringes. Unfortunately, these mammals had to be dissected to notice the change, making the process quite unwieldy and very morbid. What these laboratories needed, was an eco-friendly alternative. Enter the African clawed frog, nature's reusable pee stick.
When it was discovered that the frog also reacted to human pregnancy growth hormones, it made pregnancy testing a dream. The test was more humane, but most importantly, it was startlingly accurate. Subtle changes in a rabbit's anatomy could be difficult to interpret, but it's not hard to tell if a frog has dropped some baby bubbles. So shoot some lady pee into one's leg, fail to go to sleep, and check its tank in the morning. If the frog laid some eggs in the night, congratulations and/or condolences.
A 1938 study that used over 2,000 frogs yielded zero false positives, only a few false negatives, and a whole lot of nightmares. It's a miracle we ever switched to immunological testing kits, really. And maybe we shouldn't have. After the frogs were deemed obsolete, many battery laboratories released their ladies into the wild, introducing en masse an entirely new species to a bunch of fragile ecosystems. Since then, the African clawed frog has been found to be carriers of a deadly fungus, which has decimated around 200 other amphibian species. Let's hope we don't accidentally wipe out frog-kind because we were too lazy to keep peeing on them.