I'll also go with the deliberate hypotheses.
If I lived next door to someone who hates cats visiting their garden, and who didn't have a cat but seemed to leave containers of water out for them , I'd be mighty interested in the what and the why if cats closeby started dying after ingesting antifreeze.
Best way to keep cats out of your garden is to leave a dog in it. You still have to scoop da poop but at least a dog doesn't hide it next to your radishes
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