Some foods are genuinely dangerous, some are only a problem raw or in quantity. When in doubt, skip it and check a current sourced reference. Avoid entirely: blue cheese (the mould is toxic to rats), raw or dried beans and raw pulses, raw sweet potato, raw artichoke, green potato and potato skin/eyes, rhubarb leaves, citrus peel and, for males, large amounts of orange juice (d-limonene has been linked to kidney problems in male rats), poppy seeds, and anything mouldy. Avoid for humans-are-not-rats reasons: chocolate in any quantity worth eating, caffeine, alcohol, very salty snacks, sugary processed food, and carbonated drinks (rats cannot burp). Care needed: sticky foods like peanut butter and thick nut butters can choke a rat - smear thinly rather than spooning. Whole nuts are a choking risk for small rats. Avocado flesh is fine in small amounts but the skin, stone and leaves are not. Wild-picked greens must be free of pesticide and roadside spray. Fine, despite the myths: small amounts of cheese, bread, cooked meat, egg, most fruit and veg. New foods go in one at a time, in a small portion, so an upset stomach has an obvious cause.