Pregnancy test - Wikipedia
At the beginning of the 1930s, Hillel Shapiro and Harry Zwarenstein, who were researchers at the University of Cape Town, discovered that if urine from a pregnant female was injected into the South African Xenopus toad and the toad ovulated, this indicated that the woman was pregnant. This test was used throughout the world from the 1930s to 1960s, with Xenopus toads being exported live in great numbers. Shapiro's advisor, Lancelot Hogben, claimed to have developed the pregnancy test himself, but refuted by both Shapiro and Zwarenstein in a letter to the British Medical Journal. A later article, independently authored, granted Hogben credit for the principle of using Xenopus to determine gonadotropin levels in pregnant women's urine, but not for its usage as a functional pregnancy test.
Seriously, that’s some mad scientist territory right there. What else did they inject into toads to see what would happen?