Even though it wasn't required, Milo Ventimiglia decided he wanted to be on set when Rebecca (Mandy Moore) came in to the hospital room to see her husband's dead body. If you watched the after show, Mandy said that she hadn't expected Milo to be there and it became a very raw, very difficult scene to film.
What Milo had to say was, "I know how I am in regards to moments of experience, especially moments of experience between Jack and Rebecca. I wanted to not throw a curveball at Mandy, but I wanted to be there. It's one thing to have to act alone, it's another thing to have to take the history that she and I have worked on for two years and be a still, lifeless body in front of her. I was ultimately hearing her just break and fall to a million pieces, and that might have been the hardest thing to film, not because I had to lay still, but I was listening to my friend crumbling."
Milo also said that the camera was mostly focused on Mandy during the scene (hence why he wasn't needed on set if he hadn't wanted to be there) but he said: "You know that you can't move, you can't make a peep, you just have to be there for your scene partner and that's pretty much all I was focused on was I need to be here for Mandy. That's pretty much what our routine is in general. We're always there for one another. We kind of made a pact like that since the very beginning, like let's make this couple real."
No wonder everyone loves this show!