In Days of Heaven, Bill and Abby are actually lovers, but why does Abby tell the farmer that she and Bill are brother and sister?
1 Answer
It's a sign of the times. The movie was set in the 1910s, when extramarital sex was at least frowned upon, and an unmarried couple traveling together would arouse unwanted attention.
It could also be that, since they were on the run, they felt that acting as siblings would deter any potential suspicion.