To Take Something With a Pinch/Grain Of Salt (used as a verb)

First Example:

Lucy: Did you go to that political rally last night?
Jason: Yeah, and it was amazing! She had such great ideas, and her campaign promises are really inspiring.
Lucy: Maybe, but make sure you take anything she says with a pinch of salt.
Jason: What do you mean?
Lucy: Well, she's a politician. They're known for promising things they can't actually deliver just to get more people to vote for them.
Jason: I know, but I think she's for real.

Meaning: 

To "take (something someone says) with a pinch of salt " is a phrase that means you should be critical of what a person says. This idiom is often used when the person who says it doesn't trust something another person said, or thinks they have an ulterior motive.  In the example, Jason is excited by a political candidate, but Lucy says he should take what she says with a pinch of salt, suggesting that the candidate may be promising things she doesn't intend to deliver on.  
In addition, the word "grain" is sometimes used instead of "pinch." The idiom means the same thing with either "pinch" or "grain."

Here is another example:  
            
Bill: Want to try that restaurant that just opened?
Kelsey: I don't know; I heard their service isn't very good.              
Bill: Where did you hear that?
Kelsey: I read a review on Yelp.
Bill: Oh. Well, I take reviews on there with a grain of salt. A lot of people only write reviews if something went wrong and they want to complain.
Kelsey: True, and it got a pretty good review in the paper. Yeah, let's try it and decide for ourselves.


In this case, Bill says to take online reviews with a grain of salt, suggesting online reviews are often skewed. 

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