As a chemist, I follow laboratory safety protocol when handling all chemicals. Oxalic acid - which be be found bound-up with other chemicals in nature - is classified as a 'Corrosive' and a 'Hazardous Solid.' If a cat walked in water contaminated with OA, it would irritate their paws. And the cat would lick the area. This will corrode their GI tract and quite likely kill them.