So I assume you're all familiar with the modern method of determining whether someone is pregnant, which is to basically pee on a stick and see what the stick says. There are things you look for in blood and urine that will say whether pregnancy's taken place, and the stick looks for those. Failing that, you can also have an ultrasound and see if there's a fetus rummaging around in there.
But that's now. What were we using before urine-detecting sticks? Because we were using something... well, at least since the 1920's. Before the 20's, you pretty much had to wing it and guess. The word 'hormones' didn't even come into play until the 1890's.
We used lab animals, of course.
The first pregnancy test that didn't involve random morning sickness and observing that the missus was getting quite fat for no particular reason involved mice. In 1928, German scientists Bernhard Zondek and Selmar Aschheim noticed that when you injected urine from an early-pregnancy female into an immature female mouse, the mouse's ovaries enlarged. (The full report in California and Western Medicine is here, if you want to try to figure out the chain of events that would lead to wondering what would happen if you injected urine from an early-pregnancy female into an immature female mouse.) The thing is, in order to find that out, you had to slice the mouse open and have a look at the ovaries. After finding that you got the same result from rabbits, rabbits became the animal du jour, so much so that the phrase 'rabbit test' entered the lexicon, and the phrase 'the rabbit died' became slang term for a positive test.
Though really, the rabbits died either way. They still had to cut them up to look at the ovaries. Ah, science back in the 1930's.
Then in 1939 came the toads. This may seem like a gigantic step in the wrong direction, but quite the opposite: you could test on the toad without killing it. The toad was the African clawed toad. (Also known as African clawed frog, because how many of you can really tell anyway?) This time, the urine needed to be injected into a dorsal lymph sac, notable for being something you can reach without a whole bunch of rest-of-the-toad standing between you and it. You waited to see if eggs formed in the sac; if so, you had a pregnancy. For both toad and woman, in fact. Because the toad not only lived, but could be used over and over again, the rabbits were let off the hook. The rabbit test became the toad test until 1960, when non-animal tests were introduced and things progressed towards something suitable for home use.
After all, the kids might not appreciate wondering where their pets keep going.