Answer by  
                                                                                          traumatised (3285)
                                                            
                          
                          
                                                          It could be many things, but any amount of blood from a guinea pig is dangerous since they are so small. Take your pet to an exotics vet (who specialises in rodents, not an ordinary cat/dog vet) or emergency clinic as soon as possible for a proper check up and prognosis.