To accept or believe something only in part, with a dose of caution

Anyone knows that a dictator's propaganda should be taken with a grain of salt

Si sa bene che i discorsi di propaganda di un dittatore devono essere presi "cum grano salis"

Marcello has been known to stretch the truth a bit, so you'd better take what he says with a grain of salt and don't believe rashly to everything he says

Tutti sanno che Marcello rigira la verità a suo uso e consumo, perciò faresti meglio a prendere le sue parole con un pizzico di buon senso e non credere ciecamente a tutto quello che dice

Many believe that this expression comes from the Latin sentence "addito salis grano" (plus a grain of salt), a line used by Pliny in his "Naturalis Historia" (XXIII, ch. 77, v 3) to indicate a poison antidote that could work only if taken "with a grain of salt". Others think that the expression may refer to the fact that, in old times, salt was thought to have healing properties and to be an antidote to poison, so to eat or drink something "with a grain of salt" was to practice preventive medicine