To take something with a "grain of salt" or "pinch of salt" is an English idiom that suggests to view something, specifically claims that may be misleading or unverified, with skepticism or not to interpret something literally.[1]
In the old-fashioned English units of weight, a grain weighs approximately 65 mg, which is about how much table salt a person might pick up between the fingers as a pinch.
- ^ Webster's New World College Dictionary