During the scene involving a flock of sheep, around 60 real sheep were herded onto the studio soundstage for filming. The sheep worked perfectly for the scene, but unfortunately ate most of the plants that had been used to dress the set, meaning the production team had to spend a day locating and purchasing brand new plants that looked the same as the older ones. Source: https://the.hitchcock.zone/wiki/The_39_Steps_(1935)_-_trivia
12. Trainspotting (1996)
Ewan McGregor discussed injecting himself with heroin to better understand Renton's character with his director. Eventually they decided against it, as heroin can easily overdose someone without warning. For the close up shots of McGregor injecting himself, an entire arm was created - fully functional with pulsing veins, pockets of blood and previous injection marks. Source: http://www.imdb.com/title/tt0117951/trivia
