I was cleaning out my guinea pigs cage yesterday and found a large clump of what seemed to be fur (like a fur ball). My husband had a look at it as I was worried it might be a baby guinea pig and felt a bit squeamish. He said it felt quite hard and looked like a mix of fur and perhaps poo or nuggets. Both of my guinea pigs appear happy, are eating fine, running around, chatting normally plus there doesn't seem to be any signs of illness or pain. My only concern was that one of them chewed part of a plastic fastener and I think may have eaten it. Do guinea pigs produce fur balls? What could this 'ball' be?