Clara remains silent for most of it, or laughs whenever the Doctor teases himself. Often with a small I wasn't gonna say that but since you did. The way they always joke whenever things are serious. That's how Clara always knows that something's up, something's wrong, something's upsetting him. She can read him most times, though she spent so long with Hair that she forgets little things, and it makes her sad. Knowing that she'd lost this Doctor, her Doctor, for so long. For a long time it was just Hair and Clara and no one else, and now it's Eyebrows and Clara and no one else.
When he gets choked up over Bill and Nardole, because despite the Doctor's belief that they're another species, they are the sum of their memories. That's why Clara refused to give hers up at the end of time. She'd rather die with all of her adventures tucked safely in her head than to forget the Doctor. She reached over and takes his hand and despite his faux insistence that hugging is bad, Clara leaned against his arm and doesn't move. "I thought the worst thing I ever had to see was you forgetting me. Watching you give up this, who you are... It was hard the first time. I knew, of course I did, what with all those other lives I've got that occasionally show up in my head. But this time...