kill the rabbit

obsolete slang To receive a positive result on a pregnancy test. (From an early pregnancy test developed in 1931 in which the urine of a woman thought to be pregnant was injected into a female rabbit; if the woman was pregnant, the rabbit's ovaries would react. A common misconception at the time was that the rabbit would die if the woman was pregnant, hence the expression.) My grandmother told me that my mother had killed the rabbit. When I asked what she meant, she said that there would soon be another baby in our family, which left me even more confused!