I've never wanted to post a definition on this blog more than this one

Yesterday we spent a sweltering afternoon with my extended in-laws. One uncle in law said his wife didn't come because one of her rabbits died and she was in mourning. Two of his other uncles immediately chimed in
"Oh the rabbit's dead?! So you're pregnant?!"

We, at least all of us under 50, said "what?! He said her rabbit died!"

And they said "yeah you killed the rabbit."

kill the rabbit
1. (obsolete) (idiomatic): To get a positive test result from an old-fashioned pregnancy test.
Etymology
Before the days of instant pregnancy test, a woman's sample was injected into a rabbit. There were several varieties of tests; one alegedly would kill the rabbit if the pregnancy hormone was present in the sample (most accounts indicate the rabbit was killed and disected either way.)

(And no, she wasn't pregnant, but the rabbit really was dead.)