My daughter's pet rabbit just died. She checked it this morning and it seemed to be okay, we left for a couple of hours and when we got back it was dead. She bought it less than 24 hours ago. I check it over for signs of injury but didn't find any. Her back end was covered with what looked like diarrhea. It was black and thick. Her cage is right up against the house and the weather was not extremely hot or cold. Does anyone have any idea of what might have caused this? I want to make sure it doesn't happen to her next one.