Near the end of the movie Soylent Green, Charlton Heston’s character weeps as he accompanies his elderly friend to the suicide center.
The tears are genuine. E G Robinson was dying, and he told Charlton about it before the shoot. Charlton wasn’t acting… the emotion of the impending death of his friend was overwhelming.
Also, the whole “processing the dead into food” thing was genuine, too. The movie was over budget, so the producers cut the catering budget by eating hundreds of extras killed in various accidents on the set.
Accidents. Uh huh. Right.
Charlton laughed, and asked for seconds.