Sophie knows that the cats are a natural preditor (I didn't spell that right but I can't find it in the dictionary -- it's early!) but the guinea pig probably doesn't. My niece's guinea pig, Turnip, finds cats and dogs interesting. They look in her cage, she touches noses with them through the cage and then she goes into the igloo in her cage and looks out.

She has never appeared to be afraid and she has been observed by cats, dogs and people. We did put a top on her cage, however, when Eddie started sharing a room with her!