I noticed my 6 year old cat has been appearing slimmer than usual over the summer. He always loses quite a bit of his winter weight during the summer and quite a bit of his coat too, but it seems like it's more than he should have. His side's appear to be more caved in, but everything is completely normal. He eats, drinks, sleeps and uses the litter box just fine. He went to the vet and both of them said there's nothing wrong with him, but we weren't allowed to come inside the vets during the examination so I'm sceptical - I know it may sound silly. He walks a lot since he's an outdoor cat and my dad has told me he's seen him walk quite a way before. Could this really be the reason he looks this way or should I pursue the matter further?