"Until the mid-1960s in Britain, pregnancy tests were done by sending a woman's urine to a lab, where it would be injected into a toad"

"The toad was checked two hours later and if it had laid eggs, the woman was pregnant."

The Atlantic:

A later version of this test used rabbits instead of mice. For some reason, people came to believe that the rabbits would die if the test was positive, and the phrase “the rabbit died” became a euphemism for pregnancy. In truth, the rabbits always died, because, like the mice, they had to be dissected to check the size of their ovaries. This meant that testing for pregnancy was laborious, expensive, and bloody work. In one Pregnancy Diagnosis Station, run by a friend of Hogben’s, around 6,000 rabbits were sacrificed every year.

By comparison, the Xenopus test was faster, simpler for practitioners, and much easier on the animals. The frogs can live for up to 30 years in captivity, and since the tests didn’t kill them, they could be reused.

...

And so it was that tens of thousands of frogs were infused with human urine between the 1940s and 1960s.

...

But the frog’s rise to fame may have had an inadvertent dark side.