Can Dogs eat ...?
Food safety index

Walnuts occupy a genuinely risky middle ground for dogs — they are not acutely poisonous the way grapes are, but they carry multiple real hazards that make them unsuitable as a regular treat. Black walnuts contain juglone, a compound toxic to dogs, while all walnuts (especially older or mold-affected ones) can harbour tremorgenic mycotoxins. Even fresh English walnuts pose choking, obstruction, and pancreatitis risks due to their size and high fat content.

Kale is not acutely toxic to dogs, but it contains several naturally occurring compounds — oxalates, isothiocyanates, and calcium oxalate — that can cause digestive upset and, with large or repeated servings, more serious issues including kidney irritation and thyroid interference. Small amounts of plain kale fed occasionally are unlikely to harm a healthy adult dog. Owners of dogs with kidney disease, hypothyroidism, or a history of bladder stones should avoid kale entirely.

Spinach is not acutely toxic to dogs and offers genuine nutritional value, but it contains high levels of oxalic acid that can interfere with calcium absorption and, in large or repeated amounts, may stress the kidneys. For healthy dogs, small occasional portions are fine, but dogs with existing kidney disease or urinary problems should avoid it entirely. Moderation is the key word here.