Why a handful of shelled seeds is low-risk for a 4 kg cat
Your cat's small size doesn't magnify the risk here — the amount she ate is well below what could cause issues from the seeds themselves. The fat content might briefly unsettle her stomach if she's not used to it, but it won't overload her system. What matters more is whether any shell fragments snuck in, since those are the part that can physically irritate her digestive tract.
Compare her to your 7 kg cat who avoided them: the seeds aren't toxic in a way that would make one cat's avoidance meaningful. The real difference is that your eating cat might show mild digestive signs like one soft stool, while the other won't. Neither needs treatment unless symptoms escalate beyond what's typical for a dietary indiscretion.
When to worry about the shells you didn't see
Even if you're certain these were shelled seeds, processing plants sometimes leave tiny sharp fragments behind. At 4 kg, your cat's smaller intestines make those fragments slightly more concerning than they'd be for a larger animal. A single fragment might pass unnoticed, but multiple pieces could scrape the gut lining or, in rare cases, cluster into a minor blockage.
Watch for subtle changes like her licking her lips more than usual (signaling nausea) or taking extra trips to the litter box with little output. Straining without producing stool is more urgent than one loose bowel movement. These signs would suggest the shells — not the seeds — are causing trouble.
The next 12 hours for a seed-snacking cat
Right now, her body will treat the seeds like any unfamiliar fatty food — by trying to digest them normally. You might notice her drinking more water as her system processes the extra oil. This is harmless unless she starts refusing water altogether, which would point to nausea rather than thirst.
Offer her usual meals on schedule, but don't coax her if she skips one. A disinterest in food for over 24 hours means the seeds are bothering her more than expected, and she'd need a vet to rule out shell-related irritation. Until then, let her rest and monitor without intervening unless she vomits repeatedly or seems lethargic.
Why your other cat's size doesn't change the situation
Your 7 kg cat's avoidance of the seeds is likely just preference — their size advantage wouldn't make them safer if they had eaten the same amount. Larger cats can still react to shell fragments or fat content, just with slightly more buffer before symptoms show. Neither cat needs preventive care, but the one who ate them deserves closer watching.
If the eating cat shows no signs within eight hours, you can assume any shell fragments were negligible. The seeds themselves will pass through without lasting effect, leaving no reason to adjust either cat's routine long-term. Their shared environment needs no changes unless one starts guarding the seed stash.
The full verdict, portion guidance and serving notes are collected on the Sunflower seeds food facts page.