When was the last time you went back and took a look at documents and photographs you've not really analyzed in years?
Are there clues sitting there? Clues that you never noticed because your research skills were not as developed? Clues that you didn't realize were clues because you didn't know much about the family? Clues that you didn't notice because you simply overlooked them?
The chicken is this picture wasn't crucial to my research, but it reminded me that it never hurts to take another look.