Anyone wonder how they find body doubles for movies?

[SoCalCoug]

My son is a fledgling actor, and we subscribe to a service that is like classified ads for acting roles. I saw this one today which I thought was pretty interesting:

We are looking for two body doubles that will involve a shot from behind in your underwear. There is no nudity, and the underwear will completely cover your behind. We need doubles for Mandy Moore and Diane Keaton. In the scene the women are getting a massage, lying on their stomachs, and it will be a quick shot of their rear-ends. Mandy's sizes are: 5'9'1/2, size 6, 35Bust, 26Waist, and 38Hip. She is in her 20's. Diane's sizes are: 5'7', size 4, 34Bust, 28Waist, 36Hip, she has very slim legs. Would like a woman in her 40's. You MUST be available to go to an interview today in Venice at 5:00p.m.

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