Depends on the feather and the cat. If the feather is artificial, it is very likely it will turn up in their feces but if it's from a real bird, them it probably has some type of germ, but if you're lucky, nothing will happen.
Also, if your cat has other complications or diseases, or if your cat is little, and the feather is huge.
If the cat is bitten by the millipede while eating it, the cat could become very ill. The cat will need to be taken to a vet for treatment.
No. All cats are meat eaters. They become ill if put on a vegetarian diet.
It the person has an STD you can get the STD sexually transmitted.
if it gets it from another ill cat, or if it gets some sort of disease or illness
Yes, fleas can make a cat ill because the bites can get infected
It is an observation because you can see that the cat is ill so it is visual.
Same thing as a human, the cat will become critically ill, and the organs will start to shut down.
when a dog or cat become ill, it is always wise to take it to a vet, to make sure it is nothing serious.
ask your vet
The book on " falling ill to become healthy" is "When you fall ill".
Take it to a vet.
I think it is a inference because you are observing the cat.