You can't help worrying a bit when the cat pukes, and the litter trays show a couple of big wees and a touch of diarhoea, and he ignores breakfast and lunch, and generally sits about looking mopy.
He went out for a long time, and when he came back he had a bit of dry food.
I suppose he ate something that disagreed with him - possibly a shrew... or drank some bad water or soemthing. Or it could be a bug. Nothing serious, I guess.
When I was raspberrying, I saw a cat that was scary thin, if I'd seen it in our garden I'd have fed it probably, looked starved rather than ill. Smogg will never starve as long as there are shrews and mice about. Though he will have to get the idea that they're edible (except for the green wobbly bit)