The story
From cat + o' + nine + tails, cat referring to the inflicted wounds resembling the scratches of a cat. First attested in 1695.
Etymology from Wiktionary, CC BY-SA 4.0.
cat-o'-nine-tails
Today it means: A scourge (multi-tail whip) having nine, often knotted, whipcords, formerly used for flogging as naval punishment. Full definition →