train of thought

I was just trying to continue your train of thought.

She stopped, as though she'd lost her train of thought.

Watching this performance led to a new train of thought.

And that, in itself, set off another train of thought.

Then the voice came again, and her train of thought was gone.

But he had been following his own train of thought, which was running on a different track.

It took a moment to follow the train of thought.

What started the train of thought he did not know, but at that moment his mind was very far away.

It was clear she had lost her train of thought.

But now was not the time to lose his train of thought.