If he had a mind, there was something on it.
If men's minds were like dominoes, surely his would be the double blank.
Some minds are like soup in a poor restaurant—better left unstirred.
One of the poets, whose name I cannot recall, has a passage, which I am unable at the moment to remember, in one of his works, which for the time being has slipped my mind, which hits off admirably this age-old situation.