Perhaps you've heard the phrase, "to take something with a grain of salt." Perhaps you haven't. If the latter is the case, then I assure you that it is a fairly common and certainly standard phrase. It is a staple in phrase books no doubt.
A grain of salt. Actual size.
It means, essentially, to view something with skepticism or to not take something too seriously. For example: "The empiricist took the psychic's prediction with a grain of salt."
The idiom is derived from the Latin phrase, cum grano salis, which you can conveniently substitute for "with a grain of salt" the next time you use the phrase and want to sound like a learned scholar. So with the previous example: "The empiricist took the psychic's prediction cum grano salis... B****es."
In modern day Italy, the phrase still exists in the form, "avere sale in zucca," which translates roughly as, "to have salt in your pumpkin." Here, "pumpkin" is a metonym for "head," and the salt represents wit or intelligence (how fitting!). Similar phrases also exist in the Dutch (een korreltje zout) and Danish (et gran salt) languages.
The origin of the idiom can be attributed to this fellow,
Of course the Latin word salis happens to mean both "salt" and "wit," so maybe there was a mix-up sometime during the last 2,000 years.
The more recent phrase "to take something with a pinch of salt," dates back to F. R. Cowell's Cicero & the Roman Republic (1948):
"A more critical spirit slowly developed, so that Cicero and his friends took more than the proverbial pinch of salt before swallowing everything written by these earlier authors."
While I usually prefer things in their original, unaltered states, I certainly approve of this variation for reasons that you can probably guess (hint: it has to do with how much salt we're dealing with).