The correct idiom is "Take it with a grain of salt". It means to consider something to be not completely true or right.
According to Bloomsbury International, the idiom starts with the idea that most food tastes better with a little bit of salt. Food is tastier and therefore easier to swallow with a grain of salt, so this idiom claims that if someone is telling you something that is probably not entirely true or correct, it is easier to swallow it with a grain of salt than to argue against it.
More recently, the idiom has been modified from a grain of salt to a pinch of salt, and we can now use either grain or pinch in this saying.
Find out the 50 most useful idioms and their meaning at Smart-Words.org and discover 10 words that don't mean what you may think they do at DailyWritingTips.com.