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http://idioms.thefreedictionary.com/...rasp+at+straws
clutch/grasp at straws
1. to try any method, even those that are not likely to succeed, because you are in such a bad situation. "He's hoping that this new treatment will help him but I think he's clutching at straws."
2. to try to find reasons to feel hopeful about a situation when there is no real cause for hope. "She thinks he might still be interested because he calls her now and then but I think she's clutching at straws."