Warning: One of them involves a silicone doll.

It was a story line that resonated with several of Sullivan’s friends.

A harrowing-yet-bonding solo parenting moment with Jack in “The Cabin” proved the trickiest for Sullivan to film.

This is Us hardest scenes

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Because you certainly can’t pound your palm on the back of a real baby over and over again.

And that scene really hit me.

But two, just the emotional panic of the whole thing was hard."

This is Us cast reveals their hardest scene of season 4

NBC

(Mother would know, having delivered that I-need-you-to-be-a-10 speech to Jack in the late-’80s.)

“Anytime you push against something that you could potentially lose, it’s scary,” Metz says.

So it was really difficult.

This is Us cast reveals their hardest scene of season 4

NBC

A lot of people reached out and talked about similar experiences and it’s hard.

It’s heartbreaking."

Specifically, Sophie’s mother’s grave.

This is Us cast reveals their hardest scene of season 4

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“And for mucking that up twice.

Because I didn’t want it to be this blubbering mess.

Watson recalls the work that she put into calibrating the reactions of Deja’s adoptive, protective mother.

This is Us cast reveals their hardest scene of season 4

NBC

“It’s two families trying to protect their own,” says Watson.

“And it was hard for me because I was trying to figure out the balance.

I didn’t want it to tip into a street fight in the house.

This is Us cast reveals their hardest scene of season 4

NBC

But this thing of like, ‘Don’t step over the line either.’

That was a tricky scene to attempt to navigate the balance of that.

That was really well directed by Ken Olin, I have to say.

This is Us cast reveals their hardest scene of season 4

NBC

I love that scene.”

“Jack want[s] to be the guiding light in Randall’s life,” he says.

I’m like, ‘Jack, don’t be a jerk.

This is Us cast reveals their hardest scene of season 4

NBC

What are you doing?’

And a lot of that I think is Jack’s insecurity.

He has such a desire to be this father of their lives.

So that was tough.

Randall’s unique enough.

It has nothing to do with the color of his skin.

Let him be Randall.'”

I want to say that Pamela was absolutely wonderful to play with.

Because there’s a wall that he’s put up between him and his family.

And we’re unaccustomed to seeing it.

There’s two things that happened to me simultaneously.

There’s me performing as the actor.

So 2.0 was interesting."

“They actually shut down the museum for us to be able to film,” recalls Moore.

I had to go into this four-and-a-half page monologue.

It’s so complicated."

That knotty mix of emotions roiled inside Moore during her New York adventure.

But I have to keep that to myself.

She is so stoic and so strong.