grasp at straws字面上的意思就是抓紧稻草，引申为绝望中的挣扎。

【例句】
Harry, you're grasping at straws if you think you can pass that exam by starting to study the night before.
哈利，要是你认为在考试前一天的晚上开始念书就能通过考试的话，那你就是想捞救命稻草。

He acted like a drowning man trying to catch at a straw.
他那样做好像一个快要淹死的人拼命想捞救命稻草一样。