People outside the business think these things are one big grab-ass, but despite the subject matter, it's nothing like that. Everyone's there to do a job and major studios expect a certain level of professionalism. Especially these days.
No time for any shenanigans really. It's all rush, rush, rush then hurry up and wait. The 1st day's the most hectic. Huge cattle call, forms to fill out, releases to sign, ID's to check, etc. Everyone's given details of the shoot, a sticky label, Arse #1, Arse #2, Arse #3, etc. and photographed with it.
Day 2 was the giant parade of bare bums. Casting directors did some quick eliminations. Tats, blemishes, tan lines, wrong shape, too big, too small, wrong flesh tone, wrong sex, (several of those)... "Thanks for coming in." Those making the 1st cut are told to return the following day.
Day 3, photograph/videotape said bums. Prepare presentation. Wait for casting directors and actress, who's bum is to be portrayed to make their selections. More photographs, more deliberation, more eliminations. "Arse #5, Arse #22, Arse #57... come back tomorrow at 8AM, the rest of you thanks for coming in."
Day 4, now things are getting serious. Returning Arses must remain standing for at lease an hour sans knickers to allow time for any clothing indentations and marks to dissipate. Now, some gals will don a robe, others don't bother. Bit of a distraction that. Next it's off to make-up. Yes they have make-up for that too. More photographs, more deliberation, more elimination.
Day 5, Last 3 Arses are photographed/videotaped again and again and again, before the final selection's made.
5 days and about 60 hours to make a selection for a less than 10 second scene. Shoot, I've completed indie projects start to finish in less than half that time.
Any road, I'd be lying if I said I didn't enjoy the scenery, but between set up, making presentations and having to deal with arrogant studio folk, I was exhausted and glad to get home.