I have owned 10 cats during the last 40 years and had only once experienced a cat farting when I picked one up around her tummy. It was noisy, with no smell - just an expulsion of air it seemed. .
We have had a feral cat from our garden staying in a dog cage in our hall overnight over the last few weeks. He farts most nights, audibly and they stink! How normal is this?
(We feed him most, if not all, of his food at the moment, so I don't think he's scavenging and he doesn't poo indoors so I can't check how healthy he is from that).