The patience of a mousetrap
I woke up with the phrase, “He had the patience of a mousetrap,” in my head. As I slowly became aware of the first light of the day, I first had the impression that that probably meant very patient since a mousetrap can sit in perfect stillness for such very long periods.
Then I realized it might mean not patient at all, because even though the mousetrap might sit for long periods, it’s not doing so out of choice. And the instant anything actually interacts with it, it snaps.