lost in thought

She climbed up the stairs to the top of the tower and found him lost in thought as he looked out the window, an untouched cup of tea sitting on the table next to him.

They are all lost in thought and rarely converse with each other.

She clutches a fan in her hand and gazes pensively, lost in thought, serene, yet tinged with sadness.

His ease around people like Neil Young, Debbie Harry and Jimi Hendrix meant he often caught them in private moments, lost in thought, or playing with their pets - and there's an organic, unposed aesthetic to his work that's impossible to recreate.

I’m so lost in thought, I almost don’t see Tim.