Speaking of the frog test, there is apparently an old expression "the rabbit died" in English to refer to someone being pregnant. The original test involved injecting urine into a rabbit, killing it after a few days, and examining it's ovaries
I was watching M* A* S* H* with residents in a nursing home last week and Hot Lips thought she might be pregnant. The Colonel was concerned because they only had one rabbit and it was Radar's pet.
In case anyone is worried about the rabbit :-), they ended up using Radar's pet rabbit for the pregnancy test, but removed the ovaries surgically for examination rather than killing the rabbit.
Those weren't his words, and his actual words (which he quoted above, acknowledging their ambiguity) could be (mis)read as meaning that injecting the urine killed the rabbit a few days later, especially since he also wrote "apparently [frogs] could survive the urine injection".
I assumed that the line "can't catch me 'cause the rabbit done died" was referring to a failure to perform the rabbit test -- the rabbit they were using for the test died before the ovaries would have a chance to enlarge, therefore it was inconclusive, therefore it couldn't be proved the singer of the song got the woman in question pregnant.
https://en.m.wiktionary.org/wiki/the_rabbit_died
https://en.m.wikipedia.org/wiki/Rabbit_test
The frog was an improvement since you didn't have to kill the frog (apparently they could survive the urine injection).
FWIW the rabbit always died whether you were pregnant or not :(.