In this instance, "care" was defined as "worry" or "sorrow."
Shakespeare used a similar quote in his circa 1599 play, Much Ado About Nothing:
What, courage man! what though care killed a cat, thou hast mettle enough in thee to kill care.
Care killed the Cat. It is said that "a cat has nine lives," yet care would wear them all out.
Curiosity can do more things than kill a cat; and if emotions, well recognized as feminine, are inimical to feline life, then jealousy would soon leave the whole world catless.
CURIOSITY KILLED THE CAT.
Four Departments of New York City Government Summoned to Rescue Feline.
From the New York World.
Curiosity, as you may recall—
On the fifth floor of the apartment house at 203 West 130th street lives Miss Mable Godfrey. When she came to the house about seven months ago she brought Blackie, a cat of several years' experience of life.
The cat seldom left the apartment. He was a hearth cat, not a fence cat, and did not dearly love to sing. In other respects he was normal and hence curious.
Last Tuesday afternoon when Miss Godfrey was out Blackie skipped into the grate fireplace in a rear room. He had done this many times before. But he had not climbed up the flue to the chimney. This he did Tuesday. Blackie there remained, perched on the top of the screen separating the apartment flue from the main chimney, crying for assistance. Miss Godfrey, returning, tried to induce her pet to come down. If you are experienced in felinity, you know that Blackie didn't come down.
On Wednesday the cat, curiosity unsatisfied, tried to climb higher—and fell to the first floor. His cries could still be heard by Miss Godfrey; who, to effect Blackie's rescue, communicated with the following departments:
1. Police department.
2. Fire department.
3. Health department.
4. Building department.
5. Washington Heights court.
Among them they lowered a rope to Blackie. But it availed neither the cat nor them anything.
Thursday morning, just before noon, a plumber opened the rear wall back of the chimney. Blackie was taken out. His fall had injured his back. Ten minutes later Blackie died.
''BENNY—(with a wink) Curiosity killed a cat! Ask me no questions and I'll tell you no lies.
The full quote by Eugene O'Neill is "Curiosity killed the cat, but satisfaction brought it back."
A printed reference is included in a horoscope in the 14 September 1966 edition of The Lima News (Lima, Ohio) from (page 37):
YOUR BIRTHDAY by STELLA
LEO (July 24 - Aug. 23) — "Curiosity" Killed the cat. Let your curiosity get the best of you, find out what you want to know.