What does the term 'the rabbit died' mean?

Answer 1

It means, after a pregnancy test, the women is found to be pregnant. Around 1927 it was discovered that if you injected the urine of a pregnant woman into a rabbit, there would be corpora hemorrhagica in the ovaries of the rabbit. These bulging masses on the ovaries could not be seen with out killing the rabbit to inspect the ovaries, so invariably, every rabbit died, even if the woman wasn't pregnant. The phrase, "The rabbit died," came to be a euphemism for a positive pregnancy test after the late 1920 and early 1930s. Source: About.com

It is slang for saying someone is pregnant - the original test involved injecting an actual female rabbit with the urine of the woman who suspected she was pregnant. If the woman actually was pregnant, the rabbit would react to the pregnancy hormones - this did not kill the rabbit, but when scientists first invented this test, the only way to examine the rabbit's ovaries was to kill and dissect it. People misunderstood this whole process and thought that the rabbit died because of the pregnancy hormones. Nowadays, of course, you just buy a pregnancy test at your local drugstore.