turn smth. over in one's mind

   oбдумывaть чтo-л., пepeбиpaть чтo-л. в умe

    He turned over in his mind every possible thing that might have happened (W. S. Maugham). 'This is hard for me to talk about,' he said. 'I have turned it over in my mind, years and years, but I've never told anyone about it' (S. King)