The surprising way newborn babies are cast in movies.

Ever thought your baby could star in a movie or TV show? It’s cute enough, sure. But can it last 20 minutes without crying, crapping or nodding off?

That’s what it takes to be one of Hollywood’s unwitting stars.

Given they don’t tend to do the press circuit, little is known about Tinsel Town’s tiniest employees.

So little, in fact, that The Guardian decided to head there and find out what life is like on set.

Hollywood might be famously youth obsessed, but it does have a limit: 15 days to be exact. In fact, the Screen Actors’ Guild forbids studios to cast children any younger.

As the executive producer of smash-hit comedy Knocked Up told The Guardian, that doesn’t come without its challenges.

“Our initial intention with Knocked Up was to film a live birth,” said Evan Goldberg, “but we found out we couldn’t because the baby, by virtue of not being born yet, couldn’t be a member of SAG. So we created a fake lower body of a woman with a head that came out to simulate crowning.”

Consequently, there’s also the need to simulate other parts of childbirth. Like the goo. That strange, viscous gunk that the “newborns” are smeared with to make them appear as if they’ve been freshly delivered.

“We put grape [jam] and cream cheese on children for birthing scenes,” Goldberg said. “It’s weird.”

Knocked Up. via Universal.

Another weird aspect of the 15-day age limit, is that it means casting directors tend to favour twins and triplets to play newborns. Unsettling as it may be, they are often born prematurely and are therefore smaller. It’s essentially a way to have a brand-new baby without breaking the rules.

Of course, lookalike “spares” are also necessary for other reasons. The primary one being that infants in Hollywood are permitted only to work for four hours per day, and to be shot for just 20 minutes each hour.

An assistant director told The Guardian, “You use one baby for the first 20 minutes, a second baby for the next 20, etc. And if you’re doing a shot where the baby isn’t the focal point, or maybe it’s just in a crib in the background, you use a doll.”

Or if you’re Clint Eastwood, you just use a doll the whole time.

Remember that now-legendary scene from American Sniper? It’s an infamous industry example of why faking it doesn’t always work.

Watch Bradley Cooper explain how to make a fake baby look... less fake.

Still, there are obvious benefits to using dummies instead of kids who need them.

“When babies are on set, everyone is behaving – top of their game – because if the kid starts crying, we’re all f****d,” said Goldberg. “It’s funny to watch, like, a hundred people trying to be good parents, all at the same time."